Cut‐off value for β‐trace protein (β‐TP) as a rapid diagnostic of cerebrospinal fluid (CSF) leak detection

OBJECTIVE: To find an adequate cut‐off point for beta trace protein (β‐TP) in nasal secretion (NS) and validate this diagnostic test with a large sample of patients. Likewise, we evaluated β‐TP test efficacy to confirm the cerebrospinal fluid (CSF) leakage closure after treatment. METHODS: We performed a retrospective analysis with 207 samples from 162 patients with suspected CSF leakage received in the Hospital Universitario Virgen de la Arrixaca between 2010 and 2016. Twenty‐five samples were included in the control group. Samples were obtained from NS through a swab to determine β‐TP using a nephelometry‐based assay. Sensitivity, specificity, and area under the curve (AUC) for β‐TP in NS were assessed using the receiver operator characteristic (ROC) analysis. RESULTS: Using imaging techniques, the diagnosis of CSF leak was confirmed in 57 patients (35.19%), while 105 had a negative diagnosis (64.81%). Patients with CSF leakage had significantly higher β‐TP values in NS (16.07 ± 16.94 mg/L, p < .001) than the control group (0.33 ± 0.12 mg/L) and patients without CSF leakage (0.61 ± 2.34 mg/L). Applying a 1 mg/L cut‐off point resulted in 96.5% sensitivity and 97.1% specificity. Positive and negative predictive values (PPV and NPV) at this cut‐off were 94.9% and 98.6%, respectively. Finally, this cut‐off point yields a test efficacy for CSF leak diagnosis of 97% (95% CI 92.9–98.9). CONCLUSION: Our study has established a 1 mg/L β‐TP concentration in NS as a cut‐off point for CSF leakage diagnosis with high sensibility and specificity. These results suggest that β‐TP analysis could be useful to check CSF leak resolution. LEVEL OF EVIDENCE: 4.