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Hematuria and Proteinuria
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Hematuria and Proteinuria David Jayne | Vivian Yiu
Hematuria and proteinuria are signs of disease in the kidney or urinary tract. Their presence is often asymptomatic, so serendipitous testing of urine with dipsticks can be an important first clue indicating underlying disease. Certain populations at higher risk for kidney disease, such as patients with diabetes mellitus, undergo regular urine testing, because early detection of kidney disease is vital to prevent progression to end-stage renal disease (ESRD). Detection of hematuria and/or proteinuria should trigger further investigation and referral to the appropriate specialist (nephrologist or urologist). An understanding of the techniques of urine testing and the pathophysiology of hematuria and proteinuria, coupled with a systematic approach to the patient, are required to achieve a definitive diagnosis.
HEMATURIA DEFINITION Hematuria is the presence of erythrocytes in the urine. It can be grossly visible (macroscopic hematuria/visible hematuria) or only detectable on urine dipstick testing (microscopic hematuria/nonvisible hematuria). The degree of color change does not necessarily reflect the amount of blood in the urine, because as little as 1 mL of blood/L of urine can induce a color change. Centrifugation is the first step in analyzing red-brown urine, as hematuria is present only in the sediment. If the supernatant is red-brown, the presence of hemoglobin or myoglobin in the urine should be tested with dipsticks. Hemoglobin and myoglobin can be more accurately assessed by urinary electrophoresis. If testing is negative for heme, rare causes of urine discoloration, including porphyria, beetroot ingestion, or the use of drugs such as rifampicin, should be considered. Erythrocytes appear in low numbers in healthy individuals, but it is prudent to avoid urine testing for a few days after strenuous exertion (“jogger’s nephritis”) or menstruation. Urethral catheterization and bladder trauma can also increase the number of erythrocytes in the urine. Microscopic hematuria is defined as the presence of two or more erythrocytes per high-powered (400x) field on light microscopy in the centrifuged sediment, or less than 13,000/mL of uncentrifuged urine. Hematuria is present in up to 3% to 6% of healthy individuals, but interestingly it is present in 5% to 10% of relatives of patients with chronic kidney disease.
processes that vary with age. The most common causes include infection or inflammation of the prostate and bladder, or kidney stones. In patients over the age of 40, malignancy should be evaluated and excluded (Fig. 5.1). The American Urological Association best practice policy listed several risk factors for urologic malignancy: . Age greater than 40 years. 1 2. Smoking history (higher risk with increased exposure). 3. Occupational exposure to benzene or amine dyes (printers, painters). 4. History of gross hematuria. 5. History of chronic cystitis. 6. History of pelvic irradiation. 7. Previous cyclophosphamide use. 8. History of analgesic abuse. Damage or injury to the glomerular basement membrane (GBM) can allow the passage of red blood cells (RBCs) from the glomerular capillaries into Bowman capsule. This is often due to inflammatory conditions (glomerulonephritis—particularly IgA nephropathy and crescentic glomerulonephritis), when infiltrating leukocytes, immune complexes, or activated glomerular cells alter or rupture the GBM. It can also be a result of noninflammatory causes such as Alport syndrome, thin basement membrane disease, or diabetic nephropathy. Plasma proteins that are normally retained by the GBM often also appear in the urine, leading to associated proteinuria. Inflammation of the tubules can result in the transit of RBCs from peritubular capillaries into the tubular lumen (often accompanied by modest amounts of proteinuria) in tubulointerstitial nephritis or acute tubular necrosis, for example. Macroscopic hematuria of glomerular origin occurs in IgA nephropathy, renal vasculitis, and as a complication of anticoagulation. It can also result from secondary renal tubular damage and acute kidney injury (AKI). Persistent, isolated hematuria of glomerular origin is of prognostic significance in epidemiologic studies and confers an increased risk of ESRD. This is likely a result of four main causes:
ETIOLOGY
1. IgA nephropathy, which can be associated with macroscopic hematuria and a positive family history. 2. Alport syndrome, often associated with deafness, corneal disorders, and a positive family history. 3. Mesangioproliferative glomerulonephritis without IgA deposits. 4. Thin basement membrane disease, with a positive family history and autosomal dominant pattern of inheritance.
Macroscopic hematuria, especially if brisk and associated with clots, is most commonly associated with extraglomerular
Rare causes of hematuria include hereditary hemorrhagic telangiectasia, schistosomiasis (most notably in endemic
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CHAPTER 5 — HEMATURIA AND PROTEINURIA
Hematuria
No Other causes (e.g., drugs, pigments, hemaglobinuria, myoglobinuria)
Confirmed
Sustained
Intermittent
Infection Jogger’s nephritis Menstruation Catheter associated
Microscopic
Macroscopic
Urine microscopy for casts Throughout stream
Early in stream
Late in stream
Kidney origin
Urethral origin
Bladder or prostate origin
Present
No
Proteinuria present
No proteinuria
Glomerulonephritis
Thin membrane disease Alport syndrome
Figure 5.1 Causes of hematuria.
areas), and radiation cystitis. Arteriovenous malformations (AVMs) can be congenital or acquired and can cause macroscopic hematuria. They are often demonstrable on computed tomography (CT) scanning or angiography, where a therapeutic embolization procedure can be performed. Nutcracker syndrome, where the left renal vein is compressed between the aorta and the proximal superior mesenteric artery, can cause left flank pain, orthostatic proteinuria, and hematuria. Treatment can involve stenting of the left renal artery, or transposition of the artery. Loin pain hematuria syndrome is associated with dysmorphic RBCs and loin pain (which can be severe), but usually normal kidney function.
DETECTION A variety of findings on urinalysis favor a diagnosis of glomerular bleeding: red blood cell (RBC) casts, proteinuria exceeding 500 mg/day, and dysmorphic RBCs. These are assessed by microscopy, which can also detect other abnormalities including leukocyturia and microorganisms. A fresh urine sample should always be used, because storage can lead to erythrocyte damage. Phase-contrast microscopy or supravital staining with Eosin-Y or the Steinheimer-Malbin
stain can improve the quality of the assessment. If these techniques are unavailable, RBC morphology is best assessed using reduced illumination and adjustment of the microscope condenser to increase diffraction. Prolonged centrifugation tends to disrupt the casts, reducing the likelihood of their positive identification (Fig. 5.2). RBCs tend to be uniform and round in extrarenal sources of bleeding (normomorphic), but appear dysmorphic after traveling through the tubule in glomerular or tubular sources. In severe glomerular bleeding (i.e., IgA nephropathy or crescentic glomerulonephritis), there may be a mixture of dysmorphic and normomorphic RBCs. Very dilute urine causes osmotic lysis of RBCs forming “ghost cells.” Acanthyocytes are dysmorphic RBCs with multiple spine or bubblelike projections, typically of glomerular origin. L aboratory analysis of RBCs can quantify results (in RBCs/mL) and assess mean corpuscular volume (less than 70 fl is typical of dysmorphic hematuria). The presence of granular casts, oval fat bodies, and waxy casts together with RBC casts imply an underlying kidney lesion. Urine dipsticks impregnated with orthotolidine are very sensitive to low levels of RBCs in the urine (2 cells per highpowered field) so a positive result should be confirmed by microscopy. False positives can occur with the presence of
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SECTION 1 — STRUCTURE AND FUNCTION OF THE KIDNEYS AND THEIR CLINICAL ASSESSMENT
Hematuria suspected
Urine dipstick
Pus cells Urine microscopy
Urine culture
No casts present
RBC casts, waxy casts, dysmorphic RBCs
Urine cytology
Quantitate proteinuria Blood tests inc. eGFR, immunology screen
Kidney ultrasound
Ultrasound and/or CT scan
Kidney biopsy
Consider angiography
Consider cystoscopy
Figure 5.2 Investigation of hematuria.
hemoglobin or myoglobin. False negatives can occur if the dipsticks have been incorrectly stored or are expired, as well as in patients who consume large quantities of vitamin C. Hematuria is quantified by the number of RBCs in a spun urine sediment (RBC/high-powered field) or by counting RBCs in a hemocytometer chamber (RBCs/mL), such as the Fychs-Rosenthal chamber. The chamber avoids the loss of RBCs that may stick to the tube during centrifugation or may be discarded in the supernatant. However, there are no simple techniques to control for urine concentration.
ASSESSMENT OF THE PATIENT WITH HEMATURIA HISTORY Certain points in the patient’s history may be helpful in indicating the source of the hematuria (Table 5.1). The timing of macroscopic hematuria may provide information. Bladder lesions (e.g., schistosomiasis) tend to cause terminal hematuria, whereas urethral bleeding causes hematuria at the start of micturition. Blood from a kidney source tends to persist throughout the urinary stream. Glomerular bleeding often results in a smoky brown appearance of the urine
(“Coca-Cola urine”), whereas bladder or prostate bleeding typically results in bright red blood. The duration of hematuria, either transient or persistent, also provides important clues to etiology. Associated dysuria and frequency may suggest infection but can also be associated with acute hemorrhagic cystitis or bladder malignancy. Unilateral flank pain may indicate obstruction, either by calculus or clot (especially if the pain radiates to the groin), but can also be a sign of malignancy. Rarely it can be caused by loin pain hematuria syndrome. Hesitancy, terminal dribbling, or poor stream is indicative of prostatic obstruction in older male patients, as the new vessels formed in benign prostatic hypertrophy are fragile. A recent upper respiratory tract infection and macroscopic hematuria raise the possibility of IgA nephropathy or postinfectious glomerulonephritis. A travel history should be taken, especially to areas endemic for schistosomiasis or tuberculosis. Recent trauma, strenuous exercise, and menstruation should be excluded as causes of hematuria. Associated symptoms of edema, proteinuria (“frothy urine”), hypertension, and reduced glomerular filtration rate (GFR) suggest a glomerular cause. Previous or current symptoms
CHAPTER 5 — HEMATURIA AND PROTEINURIA
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Table 5.1 Causes of Hematuria Glomerular Hematuria Primary glomerulonephritis
Membranoproliferative glomerulonephritis Mesangioproliferative glomerulonephritis Crescentic glomerulonephritis Anti-GBM disease Focal segmental glomerulosclerosis Membranous glomerulopathy (less than 30%) Minimal change disease (less than 20%) Fibrillary glomerulopathy Multisystem or autoim- SLE Vasculitis mune disorder Scleroderma glomerulopathy Thrombotic microangiopathy Other Hereditary (Alport syndrome, Fabry disease, thin basement membrane disease) Infection associated glomerulonephritis
Urinary tract origin
Nonglomerular Hematuria Kidney origin
Tubulointerstitial nephritis Hypersensitivity tubulointerstitial nephritis TINU Sjögren syndrome Vascular disorder Malignant hypertension Renal artery or vein thrombosis AVM Scleroderma renal crisis Polyarteritis nodosa Papillary necrosis Malignancy Renal cell carcinoma Wilms tumor Lymphoma/leukemia Metastatic disease
Other
Infection Pyelonephritis Tuberculosis BK nephropathy Hereditary Polycystic kidney disease Medullary sponge kidney Trauma Idiopathic hematuria Malignancy Transitional cell carcinoma Carcinoma of the bladder/prostate Vascular Malformations/nevi Infection Cystitis Prostatitis Tuberculosis Schistosomiasis Calculi Inflammatory Retroperitoneal fibrosis/aortitis Endometriosis Diverticulitis/Crohn’s disease Hypersensitivity cystitis Vasculitis Churg-Strauss angiitis Polyarteritis nodosa Drugs Cyclophosphamide Trauma/foreign body Loin pain hematuria syndrome Acquired cystic disease of kidney failure Coagulation disorder Factitious
Anti-GBM, Antiglomerular basement membrane; AVM, arteriovenous malformation; SLE, systemic lupus erythematosus; TINU, tubulointerstitial nephritis with uveitis.
suggestive of vasculitis, diabetes mellitus, or malignancy are also useful indicators of cause. A thorough medication history to look for potential causes of nephritis, anticoagulation, or risk factors for malignancy (such as cyclophosphamide) should be obtained. A family history is important in the diagnosis of polycystic kidney disease, sickle cell anemia, and thin basement membrane disease. INVESTIGATION OF NONGLOMERULAR HEMATURIA Urine microscopy and culture enable diagnosis of most bacterial (and parasitic) infections, although sterile pyruria can occur with renal tuberculosis. If this is suspected, multiple early morning urine specimens are required for culture, as well as serum T-spot or QuantiFERON testing. Renal calculi are visible on plain radiography or noncontrast CT scanning. If stones are found, the patient requires further metabolic screening with 24-hour urine collections to identify hypercalciuria, hyperuricosuria, or hyperoxaluria. In older men, prostate-specific antigen tests and
urine cytology will help identify a malignant cause, but cystoscopy should be performed, especially if the patient is passing blood clots. The preferred imaging strategy for patients with unexplained nonglomerular hematuria is CT scanning—ideally combining conventional scanning CT with CT urography. Images of the kidney and urinary tract taken precontrast, in the renal parenchymal phase, and in the excretory phase provide a global view to look for kidney masses and transitional cell carcinomas. Ultrasonography is useful in characterizing smaller renal tumors, and angiography can be used in cases of suspected AVMs. If no cause is found, rarer diagnoses such as factitious macroscopic hematuria (which can be excluded by testing a sample voided under direct observation) or loin-pain-hematuria syndrome should be considered. Unexplained persistent hematuria requires ongoing follow-up in case serious underlying pathology emerges. Patients who have had a urothelial tumor should have screening for additional lesions in the rest of the urothelial tract.
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SECTION 1 — STRUCTURE AND FUNCTION OF THE KIDNEYS AND THEIR CLINICAL ASSESSMENT
Table 5.2 Laboratory Investigation of Glomerular Hematuria Diagnosis
Relevant Abnormal Investigations
MPGN Anti-GBM disease Fibrillary and immunotactoid glomerulopathy
C3/4, C3 nephritic factor, cryoglobulins, hepatitis B/C Anti-GBM antibodies, chest radiography Serum and urine electrophoresis, C3/C4, calcium, bone marrow biopsy, skeletal survey ANA, anti-dsDNA, ENAs, C3/4, anticardiolipin antibody ANCA: c-ANCA/PR3-ANCA or p-ANCA/MPO-ANCA
SLE Vasculitis (granulomatosis with polyangitis [Wegener], microscopic polyangiitis, Churg-Strauss angiitis) Thrombotic microangiopathy
Anticardiolipin antibody, lupus anticoagulant
Hereditary Alport disease Fabry disease
Audiometry Plasma α-galactosidase A activity
Infection Associated Glomerulonephritis HIV nephropathy Poststreptococcal glomerulonephritis Infective endocarditis
HIV ASO, anti-DNAase, C3/4, rheumatoid factor Echocardiography, C3/4, rheumatoid factor
Anti-GBM, Antiglomerular basement membrane; ANA, antinuclear antibody; ANCA, antineutrophil cytoplasmic antibody; ASO, antistreptolysin O ENAs, extractable nuclear antigens; HIV, human immunodeficiency virus; MPGN, membranoproliferative glomerulonephritis; SLE, systemic lupus erythematosus.
INVESTIGATION OF GLOMERULAR HEMATURIA Glomerular hematuria can be caused by primary glomerulonephritis or multisystem autoimmune disorders, such as systemic lupus erythematosus (SLE), vasculitis, scleroderma, and thrombotic microangiopathies. Other causes include inherited disorders (Alport syndrome, Fabry disease, thin basement membrane disease) or infection (human immunodeficiency virus [HIV]-associated nephropathy, infective endocarditis). Investigation is aimed at eliciting the severity of kidney disease, looking for extrarenal manifestations of inflammatory disease, and identifying the underlying cause (Table 5.2). Proteinuria should be quantified and urine microscopy performed to identify RBC casts. Blood tests should include a C-reactive protein (CRP), which is elevated in acute glomerulonephritis and infections. An infection screen looking for the presence of HIV and hepatitis B and C should be included if risk factors are present. In children with suspected poststreptococcal glomerulonephritis, a raised antistreptolysin O (ASO) titer and elevated anti-DNAase antibodies are usually found. A transesophageal echocardiogram to look for endocarditis and a CT scan to look for occult abscesses should also be considered if the infective source is unclear. Genetic screening is available in the case of Alport syndrome, and measurement of plasma α-galactosidase will confirm a diagnosis of Fabry disease. Immunologic investigations for patients with glomerular hematuria of unknown cause should include antinuclear antibodies (ANAs), antineutrophil cytoplasmic antibodies (ANCAs), complement levels, protein electrophoresis, and antiglomerular basement membrane (anti-GBM) antibodies if there is associated pulmonary hemorrhage, RBC casts, or deteriorating kidney function. If ANA testing
is positive, a further screen to look for related autoantibodies should be performed (see Table 5.2). Crescentic glomerulonephritis typically presents with microscopic hematuria, proteinuria greater than 100 mg/dl (2+) on urine dipstick testing, and deteriorating kidney function (Fig. 5.3). Ultrasonography is the first imaging modality used to define kidney anatomy (often as a prelude to kidney biopsy), exclude mass lesions, and demonstrate corticomedullary differentiation in acute inflammatory conditions. Doppler examination should be performed to exclude renal vein thrombosis (a cause of nonglomerular hematuria). A definitive diagnosis often requires a kidney biopsy, with samples being processed for light microscopy, immunofluorescence, and electron microscopy. The risks of the procedure need to be weighed against the benefits of a histologic diagnosis. For patients with isolated glomerular hematuria (in the absence of proteinuria or elevated serum creatinine), biopsy is usually not indicated, because the management of patients is rarely influenced by the result. The most likely diagnoses in such scenarios are IgA nephropathy or thin basement membrane disease, and specific therapy is often not warranted in the absence of adverse features.
PROTEINURIA The prevalence of proteinuria in the general population is approximately 2%, and it is higher in older individuals and those with comorbidities. Proteinuria is a marker of kidney disease, and it plays a role in screening, diagnosis, and monitoring. Large epidemiologic studies have shown that proteinuria is an independent risk factor for cardiovascular events and progressive kidney disease.
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CHAPTER 5 — HEMATURIA AND PROTEINURIA RBC casts, RPGN, Lung hemorrhage Initial screen
ANA +ve
ANCA +ve
Anti-GBM antibodies
Protein electrophoresis + Immunoglobulins
Complement
Raised RhF
Low
Anti-Ro/La +ve Antids-DNA +ve
SLE
Anti-cardiolipin antibody or lupus anticoagulant +ve
Antiphospholipid syndrome
Cryoglobulinemia ANA -ve
Anti-SCL70 or anti-RNA polymerase III +ve Sjögren syndrome Scleroderma
MPGN I
AntiMPO +ve
Microscopic polyangiitis
Raised IgA
IgA nephropathy
ANA +ve Myeloma
C3 nephritic factor
Goodpasture disease
Factor H defects
Fibrillary glomerulopathy
SLE
MPGN II
AntiPR3 +ve
Granulomatosis with polyangitis (Wegener)
Figure 5.3 Immunologic tests. ANA, Antinuclear antibody; ANCA, antineutrophil cytoplasm antibody; anti-GBM, anti-glomerular basement membrane; MPGN, membranoproliferative glomerulonephritis; RPGN, rapidly progressive glomerulonephritis; SLE, systemic lupus erythematosus.
DEFINITION Normal urinary protein excretion in an adult is less than 100 mg/24 h. Higher levels of excretion (more than 200 mg/24 h) suggest that glomerular pathology allows the passage of macromolecules such as albumin, which are not normally filtered. Excretion rates tend to increase on standing, during exertion, or with fever. Pressor agents such as angiotensin and norepinephrine tend to increase proteinuria (Table 5.3). Proteinuria is usually asymptomatic and detected by dipstick testing during routine medical examinations (e.g., with participation in high-school athletics, on entry to armed forces, or at antenatal visits). Patients often report “frothy urine” if excretion rates are high, and this is associated with hypoalbuminemia and edema as part of the nephrotic syndrome. Other causes of frothy urine include bilirubinuria, retrograde ejaculation, and pneumaturia. Protein excretion rates greater than 3000 mg/24 h are termed nephrotic range proteinuria (Fig. 5.4). In health, proteinuria results from tubular protein excretion, particularly Tamm-Horsfall protein. Albumin is the predominant protein filtered by the glomerulus, and therefore it is the most consistent marker of glomerular pathology. In health, albumin contributes little to urinary proteinuria (around 12 mg/24 h), as proteins crossing the GBM are
mainly reabsorbed and degraded via receptor-mediated endocytosis. This process shows a preference for cationic proteins and only a limited capacity for albumin, resulting in even minor glomerular abnormalities raising albuminuria. Microalbuminuria refers to albumin excretion in the range of 30 to 300 mg/24 h (20 to 200 µg/min). This equates to a urinary albumin-creatinine ratio (ACR) of 17 to 250 mg/g for men and 25 to 355 mg/g for women. Albumin and its ligands, megalin and cubulin, induce inflammatory and fibrogenic mediators, such as TGFβ, that cause tubular injury.
DETECTION AND QUANTIFICATION Urine testing using a standard dipstick relies on a colorimetric reaction between albumin and an indicator dye (such as tetrabromophenol blue or bromocrescol green) to produce a semiquantitative grading of the degree of proteinuria. As nonalbumin proteins, such as immunoglobulin light chains, are not detected, dipsticks will underestimate urine proteinuria in their presence, and dilute urine (specific gravity less than 1.005) will yield falsely low results. False positive results also occur if the urine is strongly alkaline, with pH greater than 8, thereby overwhelming the buffer on the dipstick. Inaccuracies are also seen in the presence of certain drugs
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SECTION 1 — STRUCTURE AND FUNCTION OF THE KIDNEYS AND THEIR CLINICAL ASSESSMENT
Table 5.3 Causes of Proteinuria Glomerular Proteinuria Primary glomerular disease
Secondary glomerular disease
Other
Minimal change disease IgA nephropathy Focal segmental glomerulosclerosis Membranous glomerulonephritis Membranoproliferative glomerulopathy Fibrillary and immunotactoid glomerulopathy Crescentic glomerulonephritis Multisystem disease SLE Vasculitis Amyloid Scleroderma Diabetes mellitus Malignancy Myeloma Leukemia Solid tumors Infection Bacterial Viral Fungal Parasitic Drugs Gold Penicillamine Lithium Nonsteroidals Familial Alport syndrome Nephronopthisis Fabry disease Congenital nephrotic syndrome Other Preeclampsia Transplant glomerulopathy Reflux nephropathy Febrile proteinuria Exercise-induced proteinuria (rare beyond 30 years of age) Orthostatic proteinuria
Tubular Proteinuria Drugs and toxins
Luminal injury Light chain nephropathy Lysozyme (myelogenous leukemia) Exogenous Heavy metals (lead, cadmium) Aristolochic acid (Balkan nephropathy) Tetracycline Tubulointerstitial Hypersensitivity (drugs, toxin) Systemic disease nephritis SLE Sjögren syndrome Tubulointerstitial nephritis with uveitis Other Fanconi syndrome Overflow Proteinuria Monoclonal Myeloma gammopathies Light chain disease Amyloidosis Hemoglobinuria Myoglobinuria
SLE, Systemic lupus erythematosus.
(tolbutamide, cephalosporins) and iodinated radiocontrast agents. Proteinuria on dipstick is graded from trace to 4+ as follows: Negative Trace 1+ 2+ 3+ 4+
15 to 30 mg/dl 30 to 100 mg/dl 100 to 300 mg/dl 300 to 1000 mg/dl More than 1000 mg/dl
Laboratory testings such as the biuret reaction and turbidimetry using sulfosalicylic acid (SSA) detect lower levels of proteinuria (up to 5 mg/dl) as well as nonalbumin proteins. These testings are primarily used in cases of AKI with a bland urine dipstick. A strongly positive SSA test in the presence of a negative urine dipstick indicates the presence of globulins, such as light chains. Like dipsticks, false positive results can occur with certain drugs and radiocontrast agents, so testing should not be performed within 24 hours of a contrast study. Accurate quantification of urine protein is important not only in diagnosis, but also in the management of patients with chronic kidney disease. Patients with benign isolated proteinuria typically excrete less than 1 to 2 g/day. In patients with glomerular disease, the degree of proteinuria is an important indicator of prognosis; patients with nephrotic range proteinuria have a higher risk of progression to ESRD. Response to treatment often results in a reduction in proteinuria. The gold-standard method of quantification has been a timed (usually 24 hour) urine collection. However, these collections are often fraught with inaccuracies, and it is cumbersome to transport large volumes of urine, particularly for patients with persistent proteinuria who need regular monitoring. An alternative is the use of a smaller urine volume adjusted for urinary concentration by calculating the spot protein-creatinine ratio (PCR, mg/mg or g/g). This ratio correlates with daily protein excretion expressed as g/1.73 m2 of body surface area. The most consistent results are obtained from a midstream urine specimen collected during the first urine void in the morning, but the ratio can also be applied to a random clinic sample. ACR has greater sensitivity for low-level proteinuria; however, both PCR and ACR have correlated well with 24-hour measurements in clinical trials. The normal ranges for PCR and ACR are less than 300 mg/g and less than 30 mg/g, respectively. As mentioned earlier, standard dipstick testing for protein is highly specific but not very sensitive, and it is therefore unable to detect microalbuminuria. There are specifically designed test strips for this purpose, and these should be used in screening diabetic patients as well as those with hypertension and systemic diseases such as SLE. The presence of proteinuria is an independent risk factor for the development of ESRD in patients with cardiovascular disease or a reduced GFR. However, there is currently no evidence for routine population screening, although this is performed in some countries.
ETIOLOGY Two thirds of urinary protein is filtered (glomerular proteinuria), and the remaining third is secreted (tubular
CHAPTER 5 — HEMATURIA AND PROTEINURIA
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Proteinuria suspected
Urine dipstick
Confirm with sulfosalicylic acid
Urine microscopy Quantitate proteinuria Blood tests including eGFR Urine culture
Transient
Persistent
Immunologic tests Ultrasound
Other tests normal
Reassure and discharge
<0.5 g/24 h and normal sediment
Diabetes with progressive proteinuria
Observe
>0.5 g/24 h + SLE
>1 g/24 h +/systemic disease
Nephrotic syndrome
Kidney biopsy Figure 5.4 Investigation of proteinuria. eGFR, Estimated glomerular filtration rate; SLE, systemic lupus erythematosus.
proteinuria). Glomerular proteinuria is the only type detected on urine dipsticks and is responsible for most cases of persistent proteinuria. It occurs when excess protein crosses the GBM and overwhelms the tubular reabsorption capacity. The GBM is a high-capacity ultrafiltration membrane with proteins passing across by convection or by diffusion down a concentration gradient. Mutations of podocyte cell surface proteins (such as nephrin or podocin) or of podocyte intracellular proteins that contribute to the integrity of the membrane result in proteinuria. The membrane is negatively charged because of heparin sulfates in the glomerular endothelial wall that prevent similarly charged proteins (such as albumin) from passing across. Any glomerular pathology that impairs the ability of the GBM to maintain its charge results in proteinuria. Selective proteinuria occurs when there is minimal glomerular injury (such as minimal change nephropathy), but as more damage to the GBM occurs, larger molecules contribute to proteinuria. Tubular pathology such as Dent disease, Lowe syndrome, tubulointerstitial nephritis, and heavy-metal poisoning leads
to a failure to reabsorb smaller proteins normally filtered or secreted by the renal tubules. These include α-globulins and β-globulins, (e.g., α-microglobulin and β2-microglobulin) which are detectable by urine protein electrophoresis. Proteinuria in the range of 200 to 2000 mg/24 h is seen, although mixed glomerular and tubular pathologies can coexist. Overflow proteinuria occurs when there is increased production of low molecular weight proteins that exceeds the reabsorptive capacity of the proximal tubule. The quantity of the excreted protein reflects the severity of the underlying pathology. In cases of hemolytic anemia, free hemoglobin not bound to haptoglobin appears in the urine. In rhabdomyolysis, greatly increased levels of myoglobin result in myoglobinuria.
ASSESSMENT OF THE PATIENT WITH PROTEINURIA A careful history may suggest underlying systemic or kidney disease, such as diabetes mellitus, heart failure, or previous
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SECTION 1 — STRUCTURE AND FUNCTION OF THE KIDNEYS AND THEIR CLINICAL ASSESSMENT
glomerular injury that can result in proteinuria. Examination should include measurement of blood pressure, fluid balance, and cardiac status, and an evaluation for signs of vasculitis or other systemic disease. A complete set of laboratory blood tests, including blood counts (with white cell differential) and biochemical studies for kidney function, electrolytes, albumin, globulins, cholesterol, calcium, phosphate, liver function tests, and uric acid should be sent. In addition, an immunology screen and virology testing in those patients deemed at risk is indicated. A kidney ultrasound is necessary to evaluate kidney sizes and structural abnormalities before a kidney biopsy is performed. The presence of proteinuria on a screening dipstick should be confirmed by laboratory analysis and quantification. Urine microscopy should also be performed to look for other signs of glomerular disease such as hematuria and RBC casts. The dipstick should be repeated on at least one other occasion, and if subsequent tests are negative, possible causes of false-positive results (such as radiocontrast agents) or transient proteinuria should be considered. Transient proteinuria is common, occurring in up to 4% of men and 7% of women. Vigorous exercise, fever, or the use of pressor agents can increase proteinuria. Orthostatic proteinuria should be considered in adolescent patients (frequency of 2% to 5%), but it is uncommon in those older than 30 years. It is characterized by increased protein excretion in an upright position but normal protein excretion when supine. The exact pathophysiology is unclear, but total protein excretion rarely exceeds 1 g/24 h. The diagnosis can be confirmed with a split 24-hour urine collection with urine produced during the night and during the day collected in separate containers. Orthostatic proteinuria is a benign condition that requires no further follow-up and often abates with time. Persistent proteinuria less than 2000 mg/24 h and not accompanied by worrisome features such as reduced GFR, hematuria, positive immunologic tests, or signs and symptoms of systemic disease may be observed for several months before further investigations are planned. Kidney biopsy should be considered if: • Proteinuria is of glomerular or tubular origin without a clear cause. • Progressive proteinuria is accompanied by rise in plasma creatinine. • Nephrotic range proteinuria exists. • Persistent proteinuria exists greater than 500 mg/24 h in patients with a history of SLE. • There is suspicion of vasculitis. In patients with longstanding diabetes and progressive microalbuminuria, a kidney biopsy is not justified. However, it is more difficult to evaluate a diabetic patient who suddenly develops nephrotic range proteinuria, because a minority will have other glomerular pathologies. Similarly, hypertensive patients often have low-level proteinuria, but sudden onset nephrotic syndrome often has another cause. Immunologic testing identifies circulating autoantibodies, abnormal complement levels, and pathologic immunoglobulins or immune complexes. SLE is suggested by the
presence of ANAs and antidouble stranded DNA antibodies or antibodies to extractable nuclear antigens (especially Ro, Sm, or RNP). Low complement levels typically accompany SLE. The presence of hematuria and a positive ANCA in a patient with proteinuria strongly suggests a diagnosis of microscopic polyangiitis (confirmed with a positive myeloperoxidase [MPO]-ANCA) or granulomatosis with polyangi itis (Wegener granulomatosis) (confirmed with a positive proteinase 3 [PR3]-ANCA). A positive rheumatoid factor in the setting of proteinuria is associated with cryoglobulinemia in a patient with proteinuria (see Fig. 5.3). In an older patient, occult malignancy may present as proteinuria associated with membranous nephropathy or membranoproliferative glomerulonephritis (commonly carcinoma of the breast, colon, stomach, and lung). Hodgkin and non-Hodgkin lymphomas are associated with minimal change nephropathy, and monoclonal gammopathies are associated with fibrillary glomerulopathy and overflow proteinuria. Appropriate screening with bone marrow examination, skeletal survey, CT scanning, gastrointestinal tract endoscopy, and mammography should be instigated as necessary. Myoglobinuria in the absence of muscle injury requires evaluation for drug toxicity or inherited muscle enzyme deficiency. Hemoglobinuria can be caused by intravascular hemolysis (such as paroxysmal nocturnal hemoglobinuria). Other inherited disorders such as Fabry disease may present with proteinuria. Tubular proteinuria can be quantified and monitored by assessment of the ratio of the excretion rate of β2microglobulin to that of albumin. Factitious addition of egg albumin or other proteins to the urine can be detected by urine electrophoresis. Patients with tubular proteinuria should be screened for heavy metal (cadmium, lead, antimony) toxicity and also for systemic disease (Sjögren syndrome, malignancy). BIBLIOGRAPHY Cohen RA, Brown RS: Microscopic hematuria, N Engl J Med 348: 2330-2338, 2003. Fairley K, Birch DF: A simple method for identifying glomerular bleeding, Kidney Int 21:105-108, 1982. Fogazi GB, Ponticelli C, Ritz E: The urinary sediment: an integrated view, ed 2, Oxford, 1999, Oxford University Press. Gaspari F, Perico N, Remuzzi G: Timed urine collections are not needed to measure urine protein excretion in clinical practice, Am J Kidney Dis 47:8-14, 2006. Grossfeld GD, Litwin MS, Wolf JS, et al: Evaluation of asymptomatic microscopic haematuria in adults: The American Urological Association best practice policy. Part 1: Definition, detection, prevalence and etiology, Urology 57:599-603, 2001. Grossfeld GD, Litwin MS, Wolf JS, et al: Evaluation of asymptomatic microscopic haematuria in adults: The American Urological Association best practice policy. Part 2: Patient evaluation, cytology, voided markers, imaging, cystoscopy, nephrology evaluation and follow-up, Urology 57:604-610, 2001. Hogg RJ, Furth S, Lemley KV: National Kidney Foundation’s Kidney Disease Outcomes Quality Initiative Clinical Practice Guidelines for Chronic Kidney Disease in children and adolescents: evaluation, classification and stratification, Pediatrics 111:1416-1421, 2003. National Kidney Foundation: Clinical Practice Guidelines for Chronic Kidney Disease: Evaluation Classification and Stratification. Part 4: Definition and classification of stages of chronic kidney disease, Am J Kidney Dis 39(Suppl 1):46-75, 2002.
Hematuria and Proteinuria David Jayne | Vivian Yiu
Hematuria and proteinuria are signs of disease in the kidney or urinary tract. Their presence is often asymptomatic, so serendipitous testing of urine with dipsticks can be an important first clue indicating underlying disease. Certain populations at higher risk for kidney disease, such as patients with diabetes mellitus, undergo regular urine testing, because early detection of kidney disease is vital to prevent progression to end-stage renal disease (ESRD). Detection of hematuria and/or proteinuria should trigger further investigation and referral to the appropriate specialist (nephrologist or urologist). An understanding of the techniques of urine testing and the pathophysiology of hematuria and proteinuria, coupled with a systematic approach to the patient, are required to achieve a definitive diagnosis.
HEMATURIA DEFINITION Hematuria is the presence of erythrocytes in the urine. It can be grossly visible (macroscopic hematuria/visible hematuria) or only detectable on urine dipstick testing (microscopic hematuria/nonvisible hematuria). The degree of color change does not necessarily reflect the amount of blood in the urine, because as little as 1 mL of blood/L of urine can induce a color change. Centrifugation is the first step in analyzing red-brown urine, as hematuria is present only in the sediment. If the supernatant is red-brown, the presence of hemoglobin or myoglobin in the urine should be tested with dipsticks. Hemoglobin and myoglobin can be more accurately assessed by urinary electrophoresis. If testing is negative for heme, rare causes of urine discoloration, including porphyria, beetroot ingestion, or the use of drugs such as rifampicin, should be considered. Erythrocytes appear in low numbers in healthy individuals, but it is prudent to avoid urine testing for a few days after strenuous exertion (“jogger’s nephritis”) or menstruation. Urethral catheterization and bladder trauma can also increase the number of erythrocytes in the urine. Microscopic hematuria is defined as the presence of two or more erythrocytes per high-powered (400x) field on light microscopy in the centrifuged sediment, or less than 13,000/mL of uncentrifuged urine. Hematuria is present in up to 3% to 6% of healthy individuals, but interestingly it is present in 5% to 10% of relatives of patients with chronic kidney disease.
processes that vary with age. The most common causes include infection or inflammation of the prostate and bladder, or kidney stones. In patients over the age of 40, malignancy should be evaluated and excluded (Fig. 5.1). The American Urological Association best practice policy listed several risk factors for urologic malignancy: . Age greater than 40 years. 1 2. Smoking history (higher risk with increased exposure). 3. Occupational exposure to benzene or amine dyes (printers, painters). 4. History of gross hematuria. 5. History of chronic cystitis. 6. History of pelvic irradiation. 7. Previous cyclophosphamide use. 8. History of analgesic abuse. Damage or injury to the glomerular basement membrane (GBM) can allow the passage of red blood cells (RBCs) from the glomerular capillaries into Bowman capsule. This is often due to inflammatory conditions (glomerulonephritis—particularly IgA nephropathy and crescentic glomerulonephritis), when infiltrating leukocytes, immune complexes, or activated glomerular cells alter or rupture the GBM. It can also be a result of noninflammatory causes such as Alport syndrome, thin basement membrane disease, or diabetic nephropathy. Plasma proteins that are normally retained by the GBM often also appear in the urine, leading to associated proteinuria. Inflammation of the tubules can result in the transit of RBCs from peritubular capillaries into the tubular lumen (often accompanied by modest amounts of proteinuria) in tubulointerstitial nephritis or acute tubular necrosis, for example. Macroscopic hematuria of glomerular origin occurs in IgA nephropathy, renal vasculitis, and as a complication of anticoagulation. It can also result from secondary renal tubular damage and acute kidney injury (AKI). Persistent, isolated hematuria of glomerular origin is of prognostic significance in epidemiologic studies and confers an increased risk of ESRD. This is likely a result of four main causes:
ETIOLOGY
1. IgA nephropathy, which can be associated with macroscopic hematuria and a positive family history. 2. Alport syndrome, often associated with deafness, corneal disorders, and a positive family history. 3. Mesangioproliferative glomerulonephritis without IgA deposits. 4. Thin basement membrane disease, with a positive family history and autosomal dominant pattern of inheritance.
Macroscopic hematuria, especially if brisk and associated with clots, is most commonly associated with extraglomerular
Rare causes of hematuria include hereditary hemorrhagic telangiectasia, schistosomiasis (most notably in endemic
42
43
CHAPTER 5 — HEMATURIA AND PROTEINURIA
Hematuria
No Other causes (e.g., drugs, pigments, hemaglobinuria, myoglobinuria)
Confirmed
Sustained
Intermittent
Infection Jogger’s nephritis Menstruation Catheter associated
Microscopic
Macroscopic
Urine microscopy for casts Throughout stream
Early in stream
Late in stream
Kidney origin
Urethral origin
Bladder or prostate origin
Present
No
Proteinuria present
No proteinuria
Glomerulonephritis
Thin membrane disease Alport syndrome
Figure 5.1 Causes of hematuria.
areas), and radiation cystitis. Arteriovenous malformations (AVMs) can be congenital or acquired and can cause macroscopic hematuria. They are often demonstrable on computed tomography (CT) scanning or angiography, where a therapeutic embolization procedure can be performed. Nutcracker syndrome, where the left renal vein is compressed between the aorta and the proximal superior mesenteric artery, can cause left flank pain, orthostatic proteinuria, and hematuria. Treatment can involve stenting of the left renal artery, or transposition of the artery. Loin pain hematuria syndrome is associated with dysmorphic RBCs and loin pain (which can be severe), but usually normal kidney function.
DETECTION A variety of findings on urinalysis favor a diagnosis of glomerular bleeding: red blood cell (RBC) casts, proteinuria exceeding 500 mg/day, and dysmorphic RBCs. These are assessed by microscopy, which can also detect other abnormalities including leukocyturia and microorganisms. A fresh urine sample should always be used, because storage can lead to erythrocyte damage. Phase-contrast microscopy or supravital staining with Eosin-Y or the Steinheimer-Malbin
stain can improve the quality of the assessment. If these techniques are unavailable, RBC morphology is best assessed using reduced illumination and adjustment of the microscope condenser to increase diffraction. Prolonged centrifugation tends to disrupt the casts, reducing the likelihood of their positive identification (Fig. 5.2). RBCs tend to be uniform and round in extrarenal sources of bleeding (normomorphic), but appear dysmorphic after traveling through the tubule in glomerular or tubular sources. In severe glomerular bleeding (i.e., IgA nephropathy or crescentic glomerulonephritis), there may be a mixture of dysmorphic and normomorphic RBCs. Very dilute urine causes osmotic lysis of RBCs forming “ghost cells.” Acanthyocytes are dysmorphic RBCs with multiple spine or bubblelike projections, typically of glomerular origin. L aboratory analysis of RBCs can quantify results (in RBCs/mL) and assess mean corpuscular volume (less than 70 fl is typical of dysmorphic hematuria). The presence of granular casts, oval fat bodies, and waxy casts together with RBC casts imply an underlying kidney lesion. Urine dipsticks impregnated with orthotolidine are very sensitive to low levels of RBCs in the urine (2 cells per highpowered field) so a positive result should be confirmed by microscopy. False positives can occur with the presence of
44
SECTION 1 — STRUCTURE AND FUNCTION OF THE KIDNEYS AND THEIR CLINICAL ASSESSMENT
Hematuria suspected
Urine dipstick
Pus cells Urine microscopy
Urine culture
No casts present
RBC casts, waxy casts, dysmorphic RBCs
Urine cytology
Quantitate proteinuria Blood tests inc. eGFR, immunology screen
Kidney ultrasound
Ultrasound and/or CT scan
Kidney biopsy
Consider angiography
Consider cystoscopy
Figure 5.2 Investigation of hematuria.
hemoglobin or myoglobin. False negatives can occur if the dipsticks have been incorrectly stored or are expired, as well as in patients who consume large quantities of vitamin C. Hematuria is quantified by the number of RBCs in a spun urine sediment (RBC/high-powered field) or by counting RBCs in a hemocytometer chamber (RBCs/mL), such as the Fychs-Rosenthal chamber. The chamber avoids the loss of RBCs that may stick to the tube during centrifugation or may be discarded in the supernatant. However, there are no simple techniques to control for urine concentration.
ASSESSMENT OF THE PATIENT WITH HEMATURIA HISTORY Certain points in the patient’s history may be helpful in indicating the source of the hematuria (Table 5.1). The timing of macroscopic hematuria may provide information. Bladder lesions (e.g., schistosomiasis) tend to cause terminal hematuria, whereas urethral bleeding causes hematuria at the start of micturition. Blood from a kidney source tends to persist throughout the urinary stream. Glomerular bleeding often results in a smoky brown appearance of the urine
(“Coca-Cola urine”), whereas bladder or prostate bleeding typically results in bright red blood. The duration of hematuria, either transient or persistent, also provides important clues to etiology. Associated dysuria and frequency may suggest infection but can also be associated with acute hemorrhagic cystitis or bladder malignancy. Unilateral flank pain may indicate obstruction, either by calculus or clot (especially if the pain radiates to the groin), but can also be a sign of malignancy. Rarely it can be caused by loin pain hematuria syndrome. Hesitancy, terminal dribbling, or poor stream is indicative of prostatic obstruction in older male patients, as the new vessels formed in benign prostatic hypertrophy are fragile. A recent upper respiratory tract infection and macroscopic hematuria raise the possibility of IgA nephropathy or postinfectious glomerulonephritis. A travel history should be taken, especially to areas endemic for schistosomiasis or tuberculosis. Recent trauma, strenuous exercise, and menstruation should be excluded as causes of hematuria. Associated symptoms of edema, proteinuria (“frothy urine”), hypertension, and reduced glomerular filtration rate (GFR) suggest a glomerular cause. Previous or current symptoms
CHAPTER 5 — HEMATURIA AND PROTEINURIA
45
Table 5.1 Causes of Hematuria Glomerular Hematuria Primary glomerulonephritis
Membranoproliferative glomerulonephritis Mesangioproliferative glomerulonephritis Crescentic glomerulonephritis Anti-GBM disease Focal segmental glomerulosclerosis Membranous glomerulopathy (less than 30%) Minimal change disease (less than 20%) Fibrillary glomerulopathy Multisystem or autoim- SLE Vasculitis mune disorder Scleroderma glomerulopathy Thrombotic microangiopathy Other Hereditary (Alport syndrome, Fabry disease, thin basement membrane disease) Infection associated glomerulonephritis
Urinary tract origin
Nonglomerular Hematuria Kidney origin
Tubulointerstitial nephritis Hypersensitivity tubulointerstitial nephritis TINU Sjögren syndrome Vascular disorder Malignant hypertension Renal artery or vein thrombosis AVM Scleroderma renal crisis Polyarteritis nodosa Papillary necrosis Malignancy Renal cell carcinoma Wilms tumor Lymphoma/leukemia Metastatic disease
Other
Infection Pyelonephritis Tuberculosis BK nephropathy Hereditary Polycystic kidney disease Medullary sponge kidney Trauma Idiopathic hematuria Malignancy Transitional cell carcinoma Carcinoma of the bladder/prostate Vascular Malformations/nevi Infection Cystitis Prostatitis Tuberculosis Schistosomiasis Calculi Inflammatory Retroperitoneal fibrosis/aortitis Endometriosis Diverticulitis/Crohn’s disease Hypersensitivity cystitis Vasculitis Churg-Strauss angiitis Polyarteritis nodosa Drugs Cyclophosphamide Trauma/foreign body Loin pain hematuria syndrome Acquired cystic disease of kidney failure Coagulation disorder Factitious
Anti-GBM, Antiglomerular basement membrane; AVM, arteriovenous malformation; SLE, systemic lupus erythematosus; TINU, tubulointerstitial nephritis with uveitis.
suggestive of vasculitis, diabetes mellitus, or malignancy are also useful indicators of cause. A thorough medication history to look for potential causes of nephritis, anticoagulation, or risk factors for malignancy (such as cyclophosphamide) should be obtained. A family history is important in the diagnosis of polycystic kidney disease, sickle cell anemia, and thin basement membrane disease. INVESTIGATION OF NONGLOMERULAR HEMATURIA Urine microscopy and culture enable diagnosis of most bacterial (and parasitic) infections, although sterile pyruria can occur with renal tuberculosis. If this is suspected, multiple early morning urine specimens are required for culture, as well as serum T-spot or QuantiFERON testing. Renal calculi are visible on plain radiography or noncontrast CT scanning. If stones are found, the patient requires further metabolic screening with 24-hour urine collections to identify hypercalciuria, hyperuricosuria, or hyperoxaluria. In older men, prostate-specific antigen tests and
urine cytology will help identify a malignant cause, but cystoscopy should be performed, especially if the patient is passing blood clots. The preferred imaging strategy for patients with unexplained nonglomerular hematuria is CT scanning—ideally combining conventional scanning CT with CT urography. Images of the kidney and urinary tract taken precontrast, in the renal parenchymal phase, and in the excretory phase provide a global view to look for kidney masses and transitional cell carcinomas. Ultrasonography is useful in characterizing smaller renal tumors, and angiography can be used in cases of suspected AVMs. If no cause is found, rarer diagnoses such as factitious macroscopic hematuria (which can be excluded by testing a sample voided under direct observation) or loin-pain-hematuria syndrome should be considered. Unexplained persistent hematuria requires ongoing follow-up in case serious underlying pathology emerges. Patients who have had a urothelial tumor should have screening for additional lesions in the rest of the urothelial tract.
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SECTION 1 — STRUCTURE AND FUNCTION OF THE KIDNEYS AND THEIR CLINICAL ASSESSMENT
Table 5.2 Laboratory Investigation of Glomerular Hematuria Diagnosis
Relevant Abnormal Investigations
MPGN Anti-GBM disease Fibrillary and immunotactoid glomerulopathy
C3/4, C3 nephritic factor, cryoglobulins, hepatitis B/C Anti-GBM antibodies, chest radiography Serum and urine electrophoresis, C3/C4, calcium, bone marrow biopsy, skeletal survey ANA, anti-dsDNA, ENAs, C3/4, anticardiolipin antibody ANCA: c-ANCA/PR3-ANCA or p-ANCA/MPO-ANCA
SLE Vasculitis (granulomatosis with polyangitis [Wegener], microscopic polyangiitis, Churg-Strauss angiitis) Thrombotic microangiopathy
Anticardiolipin antibody, lupus anticoagulant
Hereditary Alport disease Fabry disease
Audiometry Plasma α-galactosidase A activity
Infection Associated Glomerulonephritis HIV nephropathy Poststreptococcal glomerulonephritis Infective endocarditis
HIV ASO, anti-DNAase, C3/4, rheumatoid factor Echocardiography, C3/4, rheumatoid factor
Anti-GBM, Antiglomerular basement membrane; ANA, antinuclear antibody; ANCA, antineutrophil cytoplasmic antibody; ASO, antistreptolysin O ENAs, extractable nuclear antigens; HIV, human immunodeficiency virus; MPGN, membranoproliferative glomerulonephritis; SLE, systemic lupus erythematosus.
INVESTIGATION OF GLOMERULAR HEMATURIA Glomerular hematuria can be caused by primary glomerulonephritis or multisystem autoimmune disorders, such as systemic lupus erythematosus (SLE), vasculitis, scleroderma, and thrombotic microangiopathies. Other causes include inherited disorders (Alport syndrome, Fabry disease, thin basement membrane disease) or infection (human immunodeficiency virus [HIV]-associated nephropathy, infective endocarditis). Investigation is aimed at eliciting the severity of kidney disease, looking for extrarenal manifestations of inflammatory disease, and identifying the underlying cause (Table 5.2). Proteinuria should be quantified and urine microscopy performed to identify RBC casts. Blood tests should include a C-reactive protein (CRP), which is elevated in acute glomerulonephritis and infections. An infection screen looking for the presence of HIV and hepatitis B and C should be included if risk factors are present. In children with suspected poststreptococcal glomerulonephritis, a raised antistreptolysin O (ASO) titer and elevated anti-DNAase antibodies are usually found. A transesophageal echocardiogram to look for endocarditis and a CT scan to look for occult abscesses should also be considered if the infective source is unclear. Genetic screening is available in the case of Alport syndrome, and measurement of plasma α-galactosidase will confirm a diagnosis of Fabry disease. Immunologic investigations for patients with glomerular hematuria of unknown cause should include antinuclear antibodies (ANAs), antineutrophil cytoplasmic antibodies (ANCAs), complement levels, protein electrophoresis, and antiglomerular basement membrane (anti-GBM) antibodies if there is associated pulmonary hemorrhage, RBC casts, or deteriorating kidney function. If ANA testing
is positive, a further screen to look for related autoantibodies should be performed (see Table 5.2). Crescentic glomerulonephritis typically presents with microscopic hematuria, proteinuria greater than 100 mg/dl (2+) on urine dipstick testing, and deteriorating kidney function (Fig. 5.3). Ultrasonography is the first imaging modality used to define kidney anatomy (often as a prelude to kidney biopsy), exclude mass lesions, and demonstrate corticomedullary differentiation in acute inflammatory conditions. Doppler examination should be performed to exclude renal vein thrombosis (a cause of nonglomerular hematuria). A definitive diagnosis often requires a kidney biopsy, with samples being processed for light microscopy, immunofluorescence, and electron microscopy. The risks of the procedure need to be weighed against the benefits of a histologic diagnosis. For patients with isolated glomerular hematuria (in the absence of proteinuria or elevated serum creatinine), biopsy is usually not indicated, because the management of patients is rarely influenced by the result. The most likely diagnoses in such scenarios are IgA nephropathy or thin basement membrane disease, and specific therapy is often not warranted in the absence of adverse features.
PROTEINURIA The prevalence of proteinuria in the general population is approximately 2%, and it is higher in older individuals and those with comorbidities. Proteinuria is a marker of kidney disease, and it plays a role in screening, diagnosis, and monitoring. Large epidemiologic studies have shown that proteinuria is an independent risk factor for cardiovascular events and progressive kidney disease.
47
CHAPTER 5 — HEMATURIA AND PROTEINURIA RBC casts, RPGN, Lung hemorrhage Initial screen
ANA +ve
ANCA +ve
Anti-GBM antibodies
Protein electrophoresis + Immunoglobulins
Complement
Raised RhF
Low
Anti-Ro/La +ve Antids-DNA +ve
SLE
Anti-cardiolipin antibody or lupus anticoagulant +ve
Antiphospholipid syndrome
Cryoglobulinemia ANA -ve
Anti-SCL70 or anti-RNA polymerase III +ve Sjögren syndrome Scleroderma
MPGN I
AntiMPO +ve
Microscopic polyangiitis
Raised IgA
IgA nephropathy
ANA +ve Myeloma
C3 nephritic factor
Goodpasture disease
Factor H defects
Fibrillary glomerulopathy
SLE
MPGN II
AntiPR3 +ve
Granulomatosis with polyangitis (Wegener)
Figure 5.3 Immunologic tests. ANA, Antinuclear antibody; ANCA, antineutrophil cytoplasm antibody; anti-GBM, anti-glomerular basement membrane; MPGN, membranoproliferative glomerulonephritis; RPGN, rapidly progressive glomerulonephritis; SLE, systemic lupus erythematosus.
DEFINITION Normal urinary protein excretion in an adult is less than 100 mg/24 h. Higher levels of excretion (more than 200 mg/24 h) suggest that glomerular pathology allows the passage of macromolecules such as albumin, which are not normally filtered. Excretion rates tend to increase on standing, during exertion, or with fever. Pressor agents such as angiotensin and norepinephrine tend to increase proteinuria (Table 5.3). Proteinuria is usually asymptomatic and detected by dipstick testing during routine medical examinations (e.g., with participation in high-school athletics, on entry to armed forces, or at antenatal visits). Patients often report “frothy urine” if excretion rates are high, and this is associated with hypoalbuminemia and edema as part of the nephrotic syndrome. Other causes of frothy urine include bilirubinuria, retrograde ejaculation, and pneumaturia. Protein excretion rates greater than 3000 mg/24 h are termed nephrotic range proteinuria (Fig. 5.4). In health, proteinuria results from tubular protein excretion, particularly Tamm-Horsfall protein. Albumin is the predominant protein filtered by the glomerulus, and therefore it is the most consistent marker of glomerular pathology. In health, albumin contributes little to urinary proteinuria (around 12 mg/24 h), as proteins crossing the GBM are
mainly reabsorbed and degraded via receptor-mediated endocytosis. This process shows a preference for cationic proteins and only a limited capacity for albumin, resulting in even minor glomerular abnormalities raising albuminuria. Microalbuminuria refers to albumin excretion in the range of 30 to 300 mg/24 h (20 to 200 µg/min). This equates to a urinary albumin-creatinine ratio (ACR) of 17 to 250 mg/g for men and 25 to 355 mg/g for women. Albumin and its ligands, megalin and cubulin, induce inflammatory and fibrogenic mediators, such as TGFβ, that cause tubular injury.
DETECTION AND QUANTIFICATION Urine testing using a standard dipstick relies on a colorimetric reaction between albumin and an indicator dye (such as tetrabromophenol blue or bromocrescol green) to produce a semiquantitative grading of the degree of proteinuria. As nonalbumin proteins, such as immunoglobulin light chains, are not detected, dipsticks will underestimate urine proteinuria in their presence, and dilute urine (specific gravity less than 1.005) will yield falsely low results. False positive results also occur if the urine is strongly alkaline, with pH greater than 8, thereby overwhelming the buffer on the dipstick. Inaccuracies are also seen in the presence of certain drugs
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SECTION 1 — STRUCTURE AND FUNCTION OF THE KIDNEYS AND THEIR CLINICAL ASSESSMENT
Table 5.3 Causes of Proteinuria Glomerular Proteinuria Primary glomerular disease
Secondary glomerular disease
Other
Minimal change disease IgA nephropathy Focal segmental glomerulosclerosis Membranous glomerulonephritis Membranoproliferative glomerulopathy Fibrillary and immunotactoid glomerulopathy Crescentic glomerulonephritis Multisystem disease SLE Vasculitis Amyloid Scleroderma Diabetes mellitus Malignancy Myeloma Leukemia Solid tumors Infection Bacterial Viral Fungal Parasitic Drugs Gold Penicillamine Lithium Nonsteroidals Familial Alport syndrome Nephronopthisis Fabry disease Congenital nephrotic syndrome Other Preeclampsia Transplant glomerulopathy Reflux nephropathy Febrile proteinuria Exercise-induced proteinuria (rare beyond 30 years of age) Orthostatic proteinuria
Tubular Proteinuria Drugs and toxins
Luminal injury Light chain nephropathy Lysozyme (myelogenous leukemia) Exogenous Heavy metals (lead, cadmium) Aristolochic acid (Balkan nephropathy) Tetracycline Tubulointerstitial Hypersensitivity (drugs, toxin) Systemic disease nephritis SLE Sjögren syndrome Tubulointerstitial nephritis with uveitis Other Fanconi syndrome Overflow Proteinuria Monoclonal Myeloma gammopathies Light chain disease Amyloidosis Hemoglobinuria Myoglobinuria
SLE, Systemic lupus erythematosus.
(tolbutamide, cephalosporins) and iodinated radiocontrast agents. Proteinuria on dipstick is graded from trace to 4+ as follows: Negative Trace 1+ 2+ 3+ 4+
15 to 30 mg/dl 30 to 100 mg/dl 100 to 300 mg/dl 300 to 1000 mg/dl More than 1000 mg/dl
Laboratory testings such as the biuret reaction and turbidimetry using sulfosalicylic acid (SSA) detect lower levels of proteinuria (up to 5 mg/dl) as well as nonalbumin proteins. These testings are primarily used in cases of AKI with a bland urine dipstick. A strongly positive SSA test in the presence of a negative urine dipstick indicates the presence of globulins, such as light chains. Like dipsticks, false positive results can occur with certain drugs and radiocontrast agents, so testing should not be performed within 24 hours of a contrast study. Accurate quantification of urine protein is important not only in diagnosis, but also in the management of patients with chronic kidney disease. Patients with benign isolated proteinuria typically excrete less than 1 to 2 g/day. In patients with glomerular disease, the degree of proteinuria is an important indicator of prognosis; patients with nephrotic range proteinuria have a higher risk of progression to ESRD. Response to treatment often results in a reduction in proteinuria. The gold-standard method of quantification has been a timed (usually 24 hour) urine collection. However, these collections are often fraught with inaccuracies, and it is cumbersome to transport large volumes of urine, particularly for patients with persistent proteinuria who need regular monitoring. An alternative is the use of a smaller urine volume adjusted for urinary concentration by calculating the spot protein-creatinine ratio (PCR, mg/mg or g/g). This ratio correlates with daily protein excretion expressed as g/1.73 m2 of body surface area. The most consistent results are obtained from a midstream urine specimen collected during the first urine void in the morning, but the ratio can also be applied to a random clinic sample. ACR has greater sensitivity for low-level proteinuria; however, both PCR and ACR have correlated well with 24-hour measurements in clinical trials. The normal ranges for PCR and ACR are less than 300 mg/g and less than 30 mg/g, respectively. As mentioned earlier, standard dipstick testing for protein is highly specific but not very sensitive, and it is therefore unable to detect microalbuminuria. There are specifically designed test strips for this purpose, and these should be used in screening diabetic patients as well as those with hypertension and systemic diseases such as SLE. The presence of proteinuria is an independent risk factor for the development of ESRD in patients with cardiovascular disease or a reduced GFR. However, there is currently no evidence for routine population screening, although this is performed in some countries.
ETIOLOGY Two thirds of urinary protein is filtered (glomerular proteinuria), and the remaining third is secreted (tubular
CHAPTER 5 — HEMATURIA AND PROTEINURIA
49
Proteinuria suspected
Urine dipstick
Confirm with sulfosalicylic acid
Urine microscopy Quantitate proteinuria Blood tests including eGFR Urine culture
Transient
Persistent
Immunologic tests Ultrasound
Other tests normal
Reassure and discharge
<0.5 g/24 h and normal sediment
Diabetes with progressive proteinuria
Observe
>0.5 g/24 h + SLE
>1 g/24 h +/systemic disease
Nephrotic syndrome
Kidney biopsy Figure 5.4 Investigation of proteinuria. eGFR, Estimated glomerular filtration rate; SLE, systemic lupus erythematosus.
proteinuria). Glomerular proteinuria is the only type detected on urine dipsticks and is responsible for most cases of persistent proteinuria. It occurs when excess protein crosses the GBM and overwhelms the tubular reabsorption capacity. The GBM is a high-capacity ultrafiltration membrane with proteins passing across by convection or by diffusion down a concentration gradient. Mutations of podocyte cell surface proteins (such as nephrin or podocin) or of podocyte intracellular proteins that contribute to the integrity of the membrane result in proteinuria. The membrane is negatively charged because of heparin sulfates in the glomerular endothelial wall that prevent similarly charged proteins (such as albumin) from passing across. Any glomerular pathology that impairs the ability of the GBM to maintain its charge results in proteinuria. Selective proteinuria occurs when there is minimal glomerular injury (such as minimal change nephropathy), but as more damage to the GBM occurs, larger molecules contribute to proteinuria. Tubular pathology such as Dent disease, Lowe syndrome, tubulointerstitial nephritis, and heavy-metal poisoning leads
to a failure to reabsorb smaller proteins normally filtered or secreted by the renal tubules. These include α-globulins and β-globulins, (e.g., α-microglobulin and β2-microglobulin) which are detectable by urine protein electrophoresis. Proteinuria in the range of 200 to 2000 mg/24 h is seen, although mixed glomerular and tubular pathologies can coexist. Overflow proteinuria occurs when there is increased production of low molecular weight proteins that exceeds the reabsorptive capacity of the proximal tubule. The quantity of the excreted protein reflects the severity of the underlying pathology. In cases of hemolytic anemia, free hemoglobin not bound to haptoglobin appears in the urine. In rhabdomyolysis, greatly increased levels of myoglobin result in myoglobinuria.
ASSESSMENT OF THE PATIENT WITH PROTEINURIA A careful history may suggest underlying systemic or kidney disease, such as diabetes mellitus, heart failure, or previous
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SECTION 1 — STRUCTURE AND FUNCTION OF THE KIDNEYS AND THEIR CLINICAL ASSESSMENT
glomerular injury that can result in proteinuria. Examination should include measurement of blood pressure, fluid balance, and cardiac status, and an evaluation for signs of vasculitis or other systemic disease. A complete set of laboratory blood tests, including blood counts (with white cell differential) and biochemical studies for kidney function, electrolytes, albumin, globulins, cholesterol, calcium, phosphate, liver function tests, and uric acid should be sent. In addition, an immunology screen and virology testing in those patients deemed at risk is indicated. A kidney ultrasound is necessary to evaluate kidney sizes and structural abnormalities before a kidney biopsy is performed. The presence of proteinuria on a screening dipstick should be confirmed by laboratory analysis and quantification. Urine microscopy should also be performed to look for other signs of glomerular disease such as hematuria and RBC casts. The dipstick should be repeated on at least one other occasion, and if subsequent tests are negative, possible causes of false-positive results (such as radiocontrast agents) or transient proteinuria should be considered. Transient proteinuria is common, occurring in up to 4% of men and 7% of women. Vigorous exercise, fever, or the use of pressor agents can increase proteinuria. Orthostatic proteinuria should be considered in adolescent patients (frequency of 2% to 5%), but it is uncommon in those older than 30 years. It is characterized by increased protein excretion in an upright position but normal protein excretion when supine. The exact pathophysiology is unclear, but total protein excretion rarely exceeds 1 g/24 h. The diagnosis can be confirmed with a split 24-hour urine collection with urine produced during the night and during the day collected in separate containers. Orthostatic proteinuria is a benign condition that requires no further follow-up and often abates with time. Persistent proteinuria less than 2000 mg/24 h and not accompanied by worrisome features such as reduced GFR, hematuria, positive immunologic tests, or signs and symptoms of systemic disease may be observed for several months before further investigations are planned. Kidney biopsy should be considered if: • Proteinuria is of glomerular or tubular origin without a clear cause. • Progressive proteinuria is accompanied by rise in plasma creatinine. • Nephrotic range proteinuria exists. • Persistent proteinuria exists greater than 500 mg/24 h in patients with a history of SLE. • There is suspicion of vasculitis. In patients with longstanding diabetes and progressive microalbuminuria, a kidney biopsy is not justified. However, it is more difficult to evaluate a diabetic patient who suddenly develops nephrotic range proteinuria, because a minority will have other glomerular pathologies. Similarly, hypertensive patients often have low-level proteinuria, but sudden onset nephrotic syndrome often has another cause. Immunologic testing identifies circulating autoantibodies, abnormal complement levels, and pathologic immunoglobulins or immune complexes. SLE is suggested by the
presence of ANAs and antidouble stranded DNA antibodies or antibodies to extractable nuclear antigens (especially Ro, Sm, or RNP). Low complement levels typically accompany SLE. The presence of hematuria and a positive ANCA in a patient with proteinuria strongly suggests a diagnosis of microscopic polyangiitis (confirmed with a positive myeloperoxidase [MPO]-ANCA) or granulomatosis with polyangi itis (Wegener granulomatosis) (confirmed with a positive proteinase 3 [PR3]-ANCA). A positive rheumatoid factor in the setting of proteinuria is associated with cryoglobulinemia in a patient with proteinuria (see Fig. 5.3). In an older patient, occult malignancy may present as proteinuria associated with membranous nephropathy or membranoproliferative glomerulonephritis (commonly carcinoma of the breast, colon, stomach, and lung). Hodgkin and non-Hodgkin lymphomas are associated with minimal change nephropathy, and monoclonal gammopathies are associated with fibrillary glomerulopathy and overflow proteinuria. Appropriate screening with bone marrow examination, skeletal survey, CT scanning, gastrointestinal tract endoscopy, and mammography should be instigated as necessary. Myoglobinuria in the absence of muscle injury requires evaluation for drug toxicity or inherited muscle enzyme deficiency. Hemoglobinuria can be caused by intravascular hemolysis (such as paroxysmal nocturnal hemoglobinuria). Other inherited disorders such as Fabry disease may present with proteinuria. Tubular proteinuria can be quantified and monitored by assessment of the ratio of the excretion rate of β2microglobulin to that of albumin. Factitious addition of egg albumin or other proteins to the urine can be detected by urine electrophoresis. Patients with tubular proteinuria should be screened for heavy metal (cadmium, lead, antimony) toxicity and also for systemic disease (Sjögren syndrome, malignancy). BIBLIOGRAPHY Cohen RA, Brown RS: Microscopic hematuria, N Engl J Med 348: 2330-2338, 2003. Fairley K, Birch DF: A simple method for identifying glomerular bleeding, Kidney Int 21:105-108, 1982. Fogazi GB, Ponticelli C, Ritz E: The urinary sediment: an integrated view, ed 2, Oxford, 1999, Oxford University Press. Gaspari F, Perico N, Remuzzi G: Timed urine collections are not needed to measure urine protein excretion in clinical practice, Am J Kidney Dis 47:8-14, 2006. Grossfeld GD, Litwin MS, Wolf JS, et al: Evaluation of asymptomatic microscopic haematuria in adults: The American Urological Association best practice policy. Part 1: Definition, detection, prevalence and etiology, Urology 57:599-603, 2001. Grossfeld GD, Litwin MS, Wolf JS, et al: Evaluation of asymptomatic microscopic haematuria in adults: The American Urological Association best practice policy. Part 2: Patient evaluation, cytology, voided markers, imaging, cystoscopy, nephrology evaluation and follow-up, Urology 57:604-610, 2001. Hogg RJ, Furth S, Lemley KV: National Kidney Foundation’s Kidney Disease Outcomes Quality Initiative Clinical Practice Guidelines for Chronic Kidney Disease in children and adolescents: evaluation, classification and stratification, Pediatrics 111:1416-1421, 2003. National Kidney Foundation: Clinical Practice Guidelines for Chronic Kidney Disease: Evaluation Classification and Stratification. Part 4: Definition and classification of stages of chronic kidney disease, Am J Kidney Dis 39(Suppl 1):46-75, 2002.