β-trace protein test: new guidelines for the reliable diagnosis of cerebrospinal fluid fistula

␤-Trace protein test: New guidelines for the reliable diagnosis of cerebrospinal fluid fistula CEM MECO,

MD,

GERHARD OBERASCHER,

MD,

ERICH ARRER,

MD,

GERHARD MOSER,

MD,

and KLAUS ALBEGGER,

MD,

Salzburg,

Austria OBJECTIVE: Cerebrospinal fluid (CSF) fistulas need to be reliably diagnosed for the optimal management. Recently, in preference to ␤2-transferrin, another CSF protein, ␤-trace protein (␤TP), is similarly used with a new method for CSF diagnosis. This study evaluates the sensitive interpretation and limits of this new ␤TP test for use in routine CSF fistula diagnosis. METHODS: Nephelometric detection of ␤TP has been made in nasal secretion, serum, and CSF samples from healthy individuals as well as patients with reduced glomerular filtration rate and with bacterial meningitis. Additionally, 53 patients with suspected CSF rhinorrhea are also analyzed. RESULTS: The ␤TP test can also be used to reliably diagnose CSF rhinorrhea even slightly better than the ␤2-transferrin test. It should not be used for patients with renal insufficiency and bacterial meningitis as they substantially increase serum and decrease CSF ␤TP values, respectively. CONCLUSION: Quantitative measurement of ␤TP is a noninvasive, highly sensitive, quick, and inexpensive method that can be used for the detection of CSF rhinorrhea in nasal secretions. However, in cases where there is doubt about the interpretation, the results should be proved with ␤2-transferrin test or sodium-fluorescein test. (Otolaryngol Head Neck Surg 2003;129:508-17.)

C erebrospinal fluid (CSF) fistulas, especially of the anterior skull base, are potentially life-threatFrom the Departments of Otolaryngology–Head and Neck Surgery (Drs Meco, Oberascher, Moser, and Albegger) and Laboratory Medicine (Dr Arrer), Salzburg University Medical School. Presented at the Annual Meeting of the American Academy of Otolaryngology–Head and Neck Surgery, San Diego, CA, September 22-25, 2002. Reprint requests: Cem Meco, MD, Salzburg University Medical School, Department of Otolaryngology–Head and Neck Surgery, Mu¨llner Hauptstr 48, A-5020, Salzburg, Austria; e-mail, [email protected]. Copyright © 2003 by the American Academy of Otolaryngology–Head and Neck Surgery Foundation, Inc. 0194-5998/2003/$30.00 ⫹ 0 doi:10.1067/S0194-5998(03)01448-7 508

ening conditions if they are not diagnosed and handled properly. Those fistulas allow the free passage of intranasal bacterial flora and cause ascending contamination of the CSF, which may lead to bacterial meningitis, which is the leading cause of morbidity and mortality in these cases.1,2 A variety of etiologies cause dura lesions and CSF fistulas. Skull base fractures and iatrogenic trauma represent the most common clinical presentation, followed by neoplasms, congenital malformations, and spontaneous leaks. Reliable diagnosis of CSF from the nasal secretion (NS) is the most important cornerstone in the management of CSF fistulas and could be challenging in cases with a subclinical CSF leak. Detection of CSF proteins in the collected NS samples is routinely used for this aim. In practice, the most common used and pathognomonic one is qualitative detection of ␤2-transferrin. It has proved its value for more than 2 decades.3,4 Quantitative detection of another CSF protein, ␤-trace protein (␤TP), can also be used similarly. Recently, a new immunologic test for ␤TP detection has been introduced for CSF diagnosis in NS that achieves outcomes comparable to those of the ␤2-transferrin test.5,6 This test is based on a latex particle– enhanced immunologic assay using rabbit polyclonal antibodies against human ␤TP. If ␤TP is present in the sample, antigen-antibody complexes are formed, and in consequence, light is scattered and measured with the nephelometric device.7 A nephelometer is a device that is routinely used by the biochemists to measure plasma proteins. In our case, the intensity of scattered light depends on the amount of ␤TP in the sample. ␤TP is the second most profuse protein found in CSF after albumin, with a molecular weight of approximately 25,000 Da. Its presence in CSF was first reported in 1961.8 Later, it was found that it is mainly produced in the meninges and the choroid plexus in the central nervous system.9,10 Other than in human CSF, its presence is found in human perilymph, serum, urine, amniotic fluid, seminal

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plasma, breast cyst fluid, breast discharge fluid, milk of lactating woman, breast tumor extracts, placental extracts, fetal brain and heart tissues, and rat retinal cells.11 In 1993, it was found to be identical to prostaglandin-D (PGD) synthase, which is an enzyme responsible for the catalyzation of prostaglandin H2 (PGH2) to PGD2.12 In the central nervous system, PGD2 involves a number of different functions such as synaptic transmission, hypothalamic control of temperature, recovery from seizures, release of lutropin, and sleep induction and sedation. As an enzyme itself, it is thought to play important roles in maturation and maintenance of the central nervous system.11,13-15 Although not all of the exact functions of ␤TP (or PGD synthase) are definitively known, another function has been shown as a lipocaline. As a lipocaline, ␤TP binds with high affinity to biliverdin, bilirubin, retinaldehyde, and retinoic acid, functioning as a transport protein.11,16,17 The logic of using ␤TP for diagnosing CSF in other body fluids is based on its high concentration in CSF. More importantly, it has a reasonable and useable serum to CSF concentration gradient.5 The first study conducted with ␤TP used as a marker to detect CSF in NS was conducted in the 1980s by Felgenhauer et al.18 They were able to detect ␤TP at concentrations above 2 mg/L, allowing them to detect 10% or higher amount of CSF in the diagnostic probe. As there was no antiserum commercially available, they developed a monospecific polyclonal antibody in rabbits. Later, Bachmann et al,19 by using the same method, showed in a retrospective clinical study that ␤TP can be used to detect CSF fistulas. Nevertheless, it was still not a routinely usable diagnostic tool, as their method has the lowest limit of 2 mg/L for detecting ␤TP. It was not sensitive enough to detect lower ␤TP concentrations, which would be important for CSF diagnosis in NS. Recently, with a new test kit containing antibodies to human ␤TP that is prepared to be used with a nephelometer, it is possible to detect much smaller fractions of ␤TP concentrations in given sample fluids. Using this more advanced method, whose measurement range is sufficient to overcome earlier difficulties, ␤TP can be used as a new marker for CSF. However, because this test kit is

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available, no guidelines have been established for this test to be used in its most sensitive manner to detect ␤TP in NS. Besides, as other clinical entities like meningitis and renal diseases affect the ␤TP concentrations, there are uncertainties in the clinical application regarding the lack of interpretation guidelines. The goal of this study was to determine interpretation guidelines and limits of ␤TP test with the new test kit, while verifying them clinically for routine use of CSF fistula diagnosis in our setting. MATERIALS AND METHODS Control Groups ␤TP values in NS, serum, and CSF of healthy individuals were determined to be able to make a comparison with some specific conditions that change those values in specific pathologies. Using the Prospec nephelometer (Dade Behring, Marburg, Germany) and the N Latex ␤TP (Dade Behring, Marburg, Germany) test, ␤TP is measured in the NS of healthy subjects without any sign of CSF rhinorrhea (n ⫽ 160), in serum of healthy individuals (n ⫽ 116), and in CSF of otherwise healthy individuals, who underwent a detailed neurologic workup for various non infectious neurologic disorders (n ⫽ 19). At the time of sample collection, the sera of all have also been analyzed for serum creatinine levels, and all of them had serum creatinine levels of less than 11 mg/L in males and 9 mg/L in females, respectively, which is the upper limits of the gender-specific reference intervals. It was previously reported that the ␤TP concentrations in CSF and serum could show fluctuations from their normal values in specific disorders, like bacterial meningitis and renal insufficiencies, respectively.20,21 However, none of the earlier reports investigated the amount of these fluctuations concerning their effect on ␤TP test interpretation. This aspect is especially important when cutoff values are used for the interpretation in such a sensitive test. Therefore, to determine the influence of these pathologies and their significance on ␤TP test results, samples from different groups of patients were investigated; these include ␤TP concentrations in sera (n ⫽ 14) and NS (n ⫽ 18) of hemodialysis patients, sera (n ⫽ 11) of patients with reduced glomerular filtration rate (GFR), and

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Fig 1. Collection of NS with PVA foam nasal pledgets.

sera and CSF of acute bacterial meningitis patients (n ⫽ 3, each). Patients with a Suspected or Proven CSF rhinorrhea To evaluate the clinical efficacy of the N Latex ␤TP test for CSF fistula diagnosis in NS, from June 2000 to January 2002 all patients with a suspicion of CSF rhinorrhea were also examined for ␤TP values in their NS and sera. In our department, the diagnostic workup for dura lesions and CSF fistulas consists of ␤2-transferrin test, high-resolution computed tomography (CT), magnetic resonance (MR)-cisternography, and endoscopic and laboratory sodium fluorescein tests. Depending on the etiology and symptoms of each case, different combinations of methods are being applied on the basis of their noninvasiveness, sensitivity, specificity, and cost. For each patient, the outcome reached with the diagnostic workup, especially the ␤2-transferrin test, was compared with the findings of the ␤TP test. Diagnostic workup indicating a dura lesion or CSF fistula was proved in all patients during operative repair. Patients whose diagnoses have not been confirmed by an operation were followed up for at least 6 months. Sample Collection All NS was collected with PVA foam nasal pledgets (eg, Ivalon surgical products; Eudora,

KS; or Merocell Xomed surgical products, Jacksonville, FL), which are left in the nose for at least 4 hours and usually 6 hours. Then, the nasal pledgets underwent centrifugation for 10 minutes (2000 ⫻ g) in a metal cylinder with a mesh, which separates the probe from the pledgets as a viscous secretion (Fig 1). During the clinical trial, in case of clinical leaks, samples are collected with plastic mini– collection tubes. At the time of NS collection, serum samples of all individuals were also taken to examine serum creatinine and ␤TP for the interpretation of ␤TP test. CSF was collected from the intrathecal space through a lumbar puncture. Method Polystyrene particles coated with antibodies to human ␤TP are agglutinated when mixed with samples containing ␤TP. Then the Prospec nephelometer is used to read the value of ␤TP in the agglutination. The intensity of the scattered light in the nephelometer depends on the concentration of ␤TP in the sample, and consequently its concentration can be determined by comparison with dilutions of ␤TP standard. Reagents All needed test reagents were obtained from Dade Behring Inc. Latex␤TP Testkit was used for the quantitative determination of ␤TP. For the calibration of the nephelometer, N Protein stan-

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dard UY, which is a highly purified human CSF ␤TP, was used. In addition, N/T Protein Kontrolle LC was used for the control measurements.

All calculations were made using nontransformed data and Statistica for Windows, version 5.0 (Statsoft) statistical software.

Sample Preparation All NS samples were recentrifuged at 2000 ⫻ g in a micro–test tube (1.5 mL) for 10 minutes and measured in an automatic mode. Viscous secretions were prediluted manually to 1:100 with N Diluens buffer (10 ␮L ⫹ 1 mL) to eliminate the particles in the NS that could close the pipettes of the nephelometer and could cause false results. In this case, the usual 1:100 predilution step included in the automated procedure was omitted for such samples. For that reason, the device mode was adjusted to the special dilution of 1:1, before measurement. Then, the diluted samples were placed in the nephelometer for the measurement, and the results were read. The serum and CSF samples were measured in the automatic mode.

RESULTS Control Groups In the first line, the ␤TP values and serum creatinine levels in sera of 116 normal subjects (age, 17 to 58 years) were determined. The mean concentration (⫾SD) of ␤TP in sera of this group was 0.59 mg/L (⫾0.23; range, 0.117 to 1.44). In all individuals, creatinine values were less than 11 mg/L in males and less than 9 mg/L in females, respectively, which are the upper limits of the gender-specific reference intervals. ␤TP concentration in CSF that was normal as judged by protein, electrolyte, and cellular content was 19.6 mg/L (⫾5.8; range, 11.5 to 32.6; n ⫽ 19), and the average ratio of liquor to serum ␤TP was R ⫽ 33.2. The average concentration of ␤TP in NS of 160 subjects (age, 19 to 64 years) who had normal glomerular function (creatinine, ⬍11 mg/L in males and ⬍9 mg/L in females) and had no history or suspicion of any kind of CSF leak as well as bacterial meningitis was 0.39 mg/L (⫾0.29; range, 0.219 to 1.69) (Fig 2). In the second line, as the serum level of ␤TP is an important determinant of the cutoff value for CSF rhinorrhea screening, we have measured its concentrations in patients with conditions known or suspected to affect its serum and NS level. Because ␤TP is eliminated from the circulation mainly by glomerular filtration, we measured its concentration in hemodialysis patients and patients with reduced glomerular filtration rate (Table 1). In 14 hemodialysis patients examined, the mean serum value for ␤TP (sample collected just before hemodialysis) was clearly elevated to 11.15 mg/L (⫾2.15; range, 5.98 to 15.51) in comparison with normal subjects. Confirming previous findings,21 we also observed an elevated serum ␤TP measurement of 1.25 mg/L (⫾0.38; range, 0.83 to 2.79) in 11 patients with elevated creatinine levels (mean, 1.37 mg/dL) in serum. In addition, we measured the ␤TP concentrations in the NS of 18 hemodialysis patients (sample collected during hemodialysis). The mean ␤TP value in NS in this group was 1.05 mg/L (⫾0,70; range, 0.25 to 2.74),

Assessment As a criterion to detect CSF in the NS of healthy individuals, the statistically calculated cutoff value of 1.31 mg/L (97.5 percentile) was taken as a standpoint to discriminate between rhinorrhea and CSF rhinorrhea.5 Results between 1.31 and 1.69 mg/L (the highest value measured in controls) have been defined as limit values and should be confirmed by testing of another sample, because cutoff values are affected by preanalytical variability. Persisting results between these values with repeated ␤TP test require further investigation, either with ␤2-transferrin test or with the more sensitive sodium-fluorescein test. ␤TP values higher than 1.69 mg/L were evaluated as CSF rhinorrhea, when the serum ␤TP value was less than 1.27 mg/L (97.5 percentile). This study was conducted in collaboration with the Department of Laboratory Medicine at Salzburg University Medical School, which is equipped with a Prospec nephelometer. The measurements made reflect the reliability ranges as well as the intraassay and interassay coefficients of variation (CVs) of the method using the N Latex ␤TP test kit with a Prospec nephelometer under the laboratory conditions of the Department of Laboratory Medicine.5

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Fig 2. The 97.5 percentile of ␤TP concentration in NS from the healthy individuals (control group) with normal glomerular filtration function (creatinine values ⬍11 mg/L in males and ⬍9 mg/L in females, respectively, which is the upper limits of the gender-specific reference intervals).

Table 1. ␤-Trace protein concentrations in sera, nasal secretions (NS), and cerebrospinal fluid (CSF) of healthy individuals and patients Group

Healthy individuals

Hemodialysis patients* Hemodialysis patients† Patients with reduced GFR‡ Patients with bacterial meningitis

Specimen

n

Mean (mg/L)

SD (mg/L)

Minimum (mg/L)

Maximum (mg/L)

NS Serum CSF NS Serum Serum CSF Serum

160 116 19 18 14 11 3 3

0.39 0.59 19.6 1.05 11.15 1.25 5.27 0.60

0.29 0.23 5.8 0.70 2.15 0.38 1.11 0.19

0.22 0.12 11.5 0.25 5.98 0.83 4.10 0.38

1.69 1.44 32.6 2.74 15.51 2.79 6.30 0.72

GFR, Glomerular filtration rate. *Sample collection during hemodialysis. †Sample collection just before hemodialysis. ‡Mean serum creatinine level 1.37 mg/dL.

which is substantially higher than the normal population when compared. In the third line, as the CSF ␤TP level is also an important factor of CSF rhinorrhea screening, we measured ␤TP in CSF and serum of patients with a pathology that especially decrease the ␤TP concentration in CSF. Due to the fact that the inflammatory diseases change the protein concentrations in CSF, we determined the ␤TP concentrations in CSF and serum of patients with acute bacterial meningitis. In 3 patients with bacterial meningitis, the mean CSF

␤TP was significantly reduced to 5.27 mg/L (⫾1.11; range, 4.10 to 6.30), affirmative of earlier reports.20 The mean serum ␤TP of the same 3 patients was 0.60 mg/L (⫾0.19; range, 0.38 to 0.72) (Table 1). To perceive the change in ␤TP concentration in CSF with the therapy over time, in 1 patient with bacterial meningitis who also had subclinical signs of CSF rhinorrhea, we observed the ␤TP levels in CSF, serum, and NS. On the day of admission, the ␤TP was normal in serum (0.6 mg/L) but lower in CSF (5.3 mg/L) compared with normal CSF. The

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Fig 3. Monitoring of ␤TP in the case of acute bacterial meningitis. ␤TP values were very low on the day of admission, but rose to a almost normal level on day 7 after the administration of antibiotics. Further monitoring revealed constant levels in CSF and serum.

value in NS was 1.96 mg/L. Although on the day of admission ␤TP values in CSF were very low, after the administration of antibiotics they rose to their normal values on day 7. Further monitoring revealed constant levels in CSF and serum (Fig 3). The calculated cutoff value of 1.31 mg/L, which is the 97.5 percentile of ␤TP concentration in NS from the control group of healthy individuals (with normal glomerular filtration function), has been used as a clinically applicable criterion for the presence of CSF in NS.5 The strong deviations of ␤TP concentrations in sera and NS of patients with reduced glomerular filtration as well as a decrease in CSF during bacterial meningitis prohibit the use of the ␤TP test for these 2 population groups. The calculated cutoff values for healthy individuals cannot be used for test interpretation as reference ranges differ due to concentration gradient changes. Patients with Suspected or Proven CSF Rhinorrhea Between June 2000 and January 2002, 53 patients have been evaluated for a suspect of dura

lesion/CSF rhinorrhea in the Department of Otolaryngology, Landeskliniken Salzburg, which is a tertiary health care center. The clinical symptom and etiology– based distribution of the 53 patients is shown in Figure 4. As it can be seen, 29 of them were examined after a head trauma, whereas 7 of them were checked to clarify a possible postoperative CSF leak. In 14 patients, suspected CSF rhinorrhea was analyzed, whereas in 3 patients, a diagnostic investigation was conducted after recurrent pneumococcal meningitis or for meningoencephalocele. Of 53 patients, 10 patients had a ␤TP far above the cutoff value (1.31 mg/L), indicating a high suspicion for CSF rhinorrhea. Of those 10 patients, whose ␤TP were also above the limit value of 1.69 mg/L, the ␤2-transferrin test was able to detect all 4 with a clinical CSF rhinorrhea (2 with spontaneous CSF leaks, 1 with postoperative CSF leak, and 1 after head trauma). On the other hand, ␤2-transferrin was negative in 1 (head trauma case) of 6 patients with a subclinical CSF leak (5 after head trauma and 1 postoperative CSF rhinor-

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Fig 4. The clinical symptom and etiology– based distribution of the 53 patients with a suspicion of CSF leakage from the Department of Otorhinolaryngology.

Table 2. Comparison of ␤-trace protein test and ␤2-transferrin test results in nasal secretions (NS) of patients with a suspected or proved cerebrospinal fluid (CSF) rhinorrhea ␤TP test (N Latex ␤TP)

Head trauma Postoperative CSF fistula ? Rhinorrhea—spontaneous CSF rhinorrhea? Recurrent pneumococcal meningitis and/or meningoencephalocele

␤2-Transferrin test

Negative <1.31 mg/L

1.31 to 1.69 mg/L

Positive >1.69 mg/L

Negative

No statement

Positive

22 5 12

0 0 0

7 2 2

23 5 11

0 0 1

6 2 2

3

0

0

3

0

0

42

0 53

11

42

1 53

10

Total

rea) (Table 2). The only trauma patient with a negative ␤2-transferrin test but a highly positive ␤TP test had a subclinical CSF fistula as a result of a fracture of the ethmoid roof with bony dislocation (Fig 5). When the group of 53 patients were further evaluated, neither the ␤TP test nor the ␤2-transferrin test was able to detect 2 discrete subclinical CSF leaks in 2 trauma cases (3.8%), which could be detected with the sodium-fluorescein tests. In this group of examined patients, ␤TP test was slightly superior to the ␤2-transferrin test concerning detection of a subclinical CSF leak that ␤2transferrin test was not able to detect. It also classified a “no statement” ␤2-transferrin test result as a negative spontaneous CSF rhinorrhea. This result matches the higher analytical sensitivity of the ␤TP test. All of the patients except 1 with a positive CSF fistula finding were operated on for a dura repair in

our department, and the diagnosis was proved in all cases. The only patient who has not been operated on had an otogenic CSF rhinorrhea after acoustic neurinoma surgery and has been successfully treated with conservative methods including elevation of the head and lumbar drainage. As a common and challenging problem in CSF fistula/dura lesion diagnosis, especially after trauma, there is a group of patients in whom there is no CSF leak although there is a dura lesion. In this group of patients, logically all of the CSF diagnostic tests give a negative result. Probably, either a blood clot, mucosal edema, bony fragment, orbital tissue, brain edema, and/or prolapsed brain tissue temporarily closes the dura lesion. Of the 53 patients, 13 patients, all examined because of a head trauma, were in this group. In 4 of them, the radiologic findings like pneumatocephalus and bone dislocation of more than 3 mm (fovea, cribriform plate, sphenoid roof) indicated a dura le-

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Fig 5. After an automobile accident, a trauma patient with an anterior skull base fracture had a negative ␤2-transferrin but a highly positive ␤TP test.

sion. They have been operated on, and in 3 of them, a dura lesion was detected with the help of preoperatively applied sodium-fluorescein dye. One patient from this group who also experienced severe midface fractures was operated on primarily for mid-face reconstruction. Also, in the same session, the anterior skull base was also operated on endoscopically, and the dura was found to be intact at the site of the skull base fracture. The patients who were not operated on were followed up for at least 6 months regarding consistency of their symptoms. The ␤TP test was the main tool for this aim. During the subsequent controls, no proof of a CSF fistula/dura lesion was found. DISCUSSION Anterior skull base CSF fistulas and dura lesions are serious problems with possibly severe

complications. One of the most important steps in their management is the reliable diagnosis of CSF in the NS. Therefore there is always a stimulus to have a more sensitive CSF diagnostic test. Recently, after the introduction of the N Latex ␤TP test kit for nephelometric analysis, it is possible to detect very small amounts of CSF in NS. Nevertheless, it is also important to set guidelines for the correct clinical use, as well as to set limits for this new test. The ␤TP test is a quantitative test that relies on the concentration gradient among CSF, NS, and serum. It requires cutoff values for assessment, and those could be affected by preanalytical variability. Because of this variability, it would be more correct to discuss a high probability of assessment correctness, if the test results are around the limit values (1.31 to 1.69 mg/L). As seen in Figure 2, the majority of NS samples from normal

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individuals were far from limit values. This was also true for patients with a proved CSF fistula in our clinical trial. However, there are still samples that are between the limit values, requiring further investigation. To rule out a preanalytical mistake, in the first line the ␤TP should always be repeated; if the results persist between the limit values, they should be checked with the ␤2-transferrin or sodium-fluorescein test. Although we have not had such a case in our 53 investigated patients with a suspected CSF fistula, another important limitation for test assessment should always be kept in mind. As it is clearly revealed by 2 control groups, one with reduced glomerular filtration and the other with bacterial meningitis, ␤TP concentrations show significant variations in NS, serum, and CSF, respectively. Subjects with reduced glomerular filtration rate have elevated ␤TP up to 26 times in serum and 7 times in NS compared with healthy individuals. On the contrary, in the acute phase of a bacterial meningitis, the CSF ␤TP values decrease up to 5 times, which would automatically reduce the concentration of ␤TP in the NS samples with the same ratio in case of a CSF leak. In those very small groups of cases, logically the assessment guidelines set for normal individuals are no longer applicable. Despite those rare occasions that should be kept in mind, our results reveals a more important message. As it could be seen from the outcome of evaluated patients with a suspected CSF rhinorrhea, the quantitative ␤TP test with the criteria used for assessment is comparable to and even better than the ␤2-transferrin test, which we use as the first-line screening method for CSF diagnosis. The qualitative ␤2-transferrin test, which has been described in the 1980s in its modern form by Oberascher and Arrer,3,4 has proved its value over the decades. Since then, it has been used as the first-line screening method but also for follow-up controls of CSF leaks. For the optimal test specificity and sensitivity, the serum probes must also be tested together with the NS. It can detect 100 ␮L of CSF in 1 mL of NS, and if the test result is positive, it is pathognomonic for CSF. Although test interpretation is not easy in each case, in some requires experience for correct interpretation of the ␤2-transferrin band on the agarose gel. In

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general, a high degree of sensitivity, up to 88%, has been reported for this screening test.3,4 Nevertheless, it is not possible in all cases to reach a diagnosis only with ␤2-transferrin test, because of other factors that affect test sensitivity, such as liver cirrhosis and genetic transferrin variants. In addition, it is done manually, and reading a borderline result requires an experienced eye for correct interpretation. Therefore it is a laboratory intensive method, meaning that it take a longer time (1.5 days) to obtain the test result. On the other hand, the quantitative ␤TP test is a short, nearly fully automated test with almost no need for manual work. At the end of the test, the nephelometer reads the concentration value of ␤TP in the sample. The whole test requires less than 15 minutes, which brings the advantage of even intraoperative use. In addition, from the point of view of noninvasiveness, sample collection, and transportation, it carries all of the advantages of the ␤2-transferrin test. The reason is that there is nearly no change in the preanalytical steps. The only exception is that for sample collection, PVA foam packing (e.g., Ivalon surgical products or Merocell Xomed surgical products) can be used. No distortion has been observed on ␤TP results caused by those; they cause distortion in the ␤2transferrin test results through high protein adsorption. As these packing expand first after introduction into the nose, it is easier to place while it is also more comfortable for the patient. In addition to all of the other advantages, in comparison, the ␤TP test is nearly one third cheaper than the ␤2-transferrin test. In our hospital, the cost per examination for the ␤2-transferrin test is $50, whereas it is only $20 for the ␤TP test. More important, the ␤TP test has all of the essential advantages of the ␤2-transferrin test. Of great consequence, it is also a noninvasive test. It can be used anytime and is easily repeated; also, it can be used in comatose patients without a concern for complications. Furthermore, easy sample collection and transportation enable a wide area of application, including disciplines other than otorhinolaryngology. Even the patient could collect the NS at home in a plastic test tube and post it to the physician if an intermittent CSF leak is suspected.

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CONCLUSION The new quantitative ␤TP test is a noninvasive, highly sensitive, and quick method that can be used as a marker for the detection of CSF rhinorrhea in NS. Moreover, its ease in handling and low cost make it an economically valuable tool to replace the ␤2-transferrin test as the modern screening test for CSF fistula and dura lesions. It also incorporates every substantial advantage of the qualitative ␤2-transferrin test, including easy sample collection (also from unconscious patients), integration of other specialties (ie, neurosurgeons, maxillofacial and trauma surgeons) to CSF diagnosis, ability to mail samples, noninvasiveness, lack of complications, and repeatability. It should be kept in mind, however, that the ␤TP test is not a suitable test for patients with bacterial meningitis and those with reduced glomerular filtration. For a few patients who have repeat ␤TP values between 1.31 and 1.69 mg/L in the NS, further CSF diagnosis investigation should be undertaken with the ␤2-transferrin and/or sodiumfluorescein test. Through its proven advantages and reliability, the ␤TP test is favored as the new, first-line CSF fistula screening test in our hands. REFERENCES

1. Bernal-Sprekelsen M, Bleda-Vazquez C, Carrau RL. Ascending meningitis secondary to traumatic cerebrospinal fluid leaks. Am J Rhinol 2000;14:257-9. 2. Hilary AB. Prophylactic antibiotics for posttraumatic cerebrospinal fluid fistula. A meta-analysis. Arch Otolaryngol Head Neck Surg 1997;123:749-52. 3. Oberascher G, Arrer E. Efficiency of various methods of identifying cerebrospinal fluid in oto- and rhinorrhea. Otorhinolaryngology 1986;48:320-5. 4. Oberascher G. A modern concept of cerebrospinal fluid diagnosis in oto- and rhinorrhea. Rhinology 1988;26:89102. 5. Arrer E, Meco C, Oberascher G, et al. ␤-Trace protein as a marker for cerebrospinal fluid rhinorrhea. Clin Chem 2002;48:939-41. 6. Petereit HF, Bachmann G, Nekic M, et al. A new nephelometric assay for ␤-trace protein (prostaglandin D syn-

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