A Sweet Cause of Polyuria

Correspondence Table 1. Pseudohyperkalemia in a CLL Patient and Testing of Possible Causative Factors Technique and Samplea

Needle Gauge

Mode of Transport

Peripheral venous sample drawn with butterfly Peripheral venous sample drawn with butterfly Peripheral venous sample drawn with butterfly

23 23 23

Pneumatic tube transport Pneumatic tube transport Pneumatic tube transport

Time Sample Drawn

Sodium Heparin

01:30 (initial presentation) 04:00 06:19

No Yes Yes

Potassium (mEq/L)

Initial Laboratory Analysis 5.5 (slightly hemolyzed) 7.5 8.0

Testing of Parameters Leading to Pseudohyperkalemia Radial arterial sample (heparinized ABG syringe, sent on ice) Peripheral venous sample drawn with butterfly (tourniquet, no ice) Peripheral venous sample drawn with butterfly (tourniquet, no ice) Radial arterial sample (heparinized ABG syringe, sent on ice) Femoral venous sample (no tourniquet, sent on ice) Femoral venous sample (no tourniquet, no ice) Femoral venous sample (no tourniquet, no ice)

18

Hand carried to laboratory

4.1

08:20

Yes

23

Pneumatic tube transport

5.6

08:40

Yes

23

Hand carried to laboratory

3.5

10:53

Yes

23

Hand carried to laboratory

3.3

11:20

Yes

18

Hand carried to laboratory

3.6

11:25

Yes

18

Hand carried to laboratory

3.9

11:28

Yes

18

Pneumatic tube transport

6.6 (hemolyzed)

11:30

Yes

Note: Reference range for potassium is 3.5-5.0 mEq/L; no conversion is necessary for serum potassium in mEq/L and mmol/L. Abbreviations: ABG, arterial blood gas; CLL, chronic lymphocytic leukemia. a All blood samples were analyzed using the Siemens Rapid Lab 865 Blood Gas Analyzer.

quent samples (Table 1). The patient had known baseline left bundle branch block, occasional premature ventricular complexes, and first-degree heart block. The electrocardiogram obtained on admission was unchanged compared with previous electrocardiograms and was not usable to exclude changes from hyperkalemia. Given the history of CLL, we suspected pseudohyperkalemia, an entity that has been attributed variably to pneumatic tube transport of samples, use of vacuum tubes, and disparities between venous and arterial blood draws (with potassium concentration higher in venous samples).1-5 It is unclear which factor is more important. To explore the most accurate means of determining our patient’s potassium concentration, we compared levels from both arterial and venous sites. We also compared potassium measurement under different conditions of blood draw technique, sample handing, and transportation (Table 1). We used heparinized tubes for all subsequent draws to minimize sample clotting as a possible confounder. As shown in the table, we show that in pseudohyperkalemia due to CLL, arterial sampling may not be needed, with reliable measurements of serum potassium potentially obtained through venous draws, even with use of a tourniquet, as long as extreme care is taken in technique and method of transport. Simran K. Sindhu John K. Hix William Fricke Rochester General Hospital Rochester, New York

Acknowledgements The corresponding author, Dr Hix, may be contacted at [email protected]. Support: None. Financial Disclosure: The authors declare that they have no relevant financial interests. Am J Kidney Dis. 2011;57(2):352-359

References 1. Kellerman PS, Thornberry JM. Pseudohyperkalemia due to pneumatic tube transport in a leukemic patient. Am J Kidney Dis. 2005;46:746-748. 2. Ruddy KJ, Wu D, Brown JR. Pseudohyperkalemia in chronic lymphocytic leukemia. J Clin Oncol. 2008;16:2781-2782. 3. Kim A, Biteman B, Malik UF, et al. A case of pseudohyperkalemia in a patient presenting with leucocytosis and high potassium level: a case report. Cases J. 2010;3:73. 4. Smalley R, Cook S, Chan M. The case best not shaken or stirred! Chronic lymphocytic leukemia and hyperkalemia. Kidney Int. 2010;77:167-168. 5. Colussi G. Pseudohyperkalemia in leukemias. Am J Kidney Dis. 2006;47(2):373. © 2011 by the National Kidney Foundation, Inc. doi:10.1053/j.ajkd.2010.11.014

A Sweet Cause of Polyuria To the Editor: Because of the growing market for “diet” or “light” foods, consumption of artificial sweeteners in Western countries continues to increase. We describe a case that illustrates the effects of a massive intake of sweeteners on plasma osmolality and water balance. A 41-year-old woman with a history of anorexia nervosa was transferred to our hospital from a psychiatric institution with polydipsia and polyuria (urine output ⬎5 L/d). Laboratory findings showed increased plasma osmolality (363 mOsm/kg) with urine osmolality of 388 mOsm/kg, consistent with osmotic diuresis. Despite a serum sodium level of 120 mmol/L, natriuresis was high (sodium excretion of 45 mmol/L [⬎200 mmol/d]). Urea and glucose levels were unremarkable, resulting in a high urine osmolal gap of 94 mOsm/kg and investigation into the presence of an exogenous solute. 355

Correspondence

Polyuria Urine osmolality < 300 mosm/kg

Urine osmolality > 300 mosm/kg

Non-osmo
c diuresis Water restric
on test: Urine osmolality < 300 mosm/kg Plasma osmolality > 300 mosm/kg

Diabetes insipidus

Osmo
c diuresis

Water restric
on test: Plasma osmolality in normal range

Psychogenic Polydipsia

Osmolal gap < 10 mosm/kg

Endogenous solutes, eg, hyperglycemia

Osmolal gap > 10 mosm/kg

Exogenous solutes

Figure 1. Simplified diagnostic approach to polyuria. The urine osmolal gap differentiates between endogenous and exogenous solutes in osmotic polyuria. Definitions based on Dashe et al.1

The answer was directly in front of our eyes. Or actually it was not, because every artificial sweetener suddenly disappeared from our ward from the day of the patient’s admission. Thorough anamnesis showed daily consumption of 1 box (600 sachets) of a common artificial sweetener and 3 L of Diet Coke. Saccharin and cyclohexylamine, a metabolite of cyclamate, initially were detectable using high-performance liquid chromatography in plasma and disappeared after withdrawal of the sweetener; subsequently, there was normalization of plasma osmolality and urine volume. The present case shows that artificial sweeteners and their metabolites are osmotically active compounds. Furthermore, it shows that plasma osmolal gap is a useful tool to distinguish endogenous and exogenous solutes in osmotic polyuria (Fig 1). Felix S. Seibert, MD1 Benno Riesselmann, MD2 Timm H. Westhoff, MD1 1 Charité–Campus Benjamin Franklin 2 State Institute of Legal and Social Medicine Berlin, Germany

Acknowledgements The corresponding author, Dr Westhoff, may be contacted at [email protected]. Support: None. Financial Disclosure: The authors declare that they have no relevant financial interests.

Reference

cae obstructing some of the other catheter holes. In addition, necrotic debris, probably secondary to necrosis of either the ovarian fimbria or appendices epiploicaes, also were obstructing the catheter lumen (Fig 1). In view of repeated obstruction of the catheter and the patient’s dependence on PD therapy, a partial fimbriectomy was undertaken after consultation with the entire medical team and parents. One year later, the PD catheter continues to function well. Although obstruction of a PD catheter by an ovarian fimbria has been reported, a MEDLINE search showed only a single previous report in children.1-3 Fimbriectomy to prevent recurrence of PD catheter obstruction can be an option in the elderly,4,5 but needs to be discussed fully and debated in children. This report highlights the need to be aware of this unusual cause of catheter blockage even in children, as well as the ethical problem of balancing the risk of future infertility with possible discontinuation of a lifesustaining procedure in a young girl. Rajiv Sinha, MD, FRCPCH CCT (Paed Nephrology) AMRI Hospitals Kolkata, India Arindam Dastidar, MS, Mch (Paediatric Surgery) Christian Medical College Vellore, India

Acknowledgements The corresponding author, Dr Sinha, may be contacted at [email protected]

1. Dashe AM, Cramm RE, Crist CA, Habener JF, Solomon DH. A water deprivation test for the differential diagnosis of polyuria. JAMA. 1963;185:699-703. © 2011 by the National Kidney Foundation, Inc. doi:10.1053/j.ajkd.2010.11.016

Obstruction of a Peritoneal Dialysis Catheter by an Ovarian Fimbria in a 2-Year-Old Girl To the Editor: Laparoscopy of a nonfunctioning peritoneal dialysis (PD) catheter in a 2-year-old girl receiving continuous ambulatory PD showed it to be blocked by an ovarian fimbria of the left fallopian tube. The fimbriae were repositioned and the catheter started draining well. The problem recurred within a week and repeated laparoscopy showed the catheter to be blocked once more by the fimbria. This again was freed and normal drainage was restored, but it started malfunctioning after a month. Laparoscopy again showed recurrence of the problem along with appendices epiploi356

Figure 1. Image shows (A) ovarian fimbria and (B) appendices epiplocea blocking the holes in a peritoneal dialysis catheter. (C) Necrotic debris is visible in the lumen. Am J Kidney Dis. 2011;57(2):352-359