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 (beta-TP) in nasal secretion (NS) and validate this diagnostic test with a large sample of patients. Likewise, we evaluated beta-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 beta-TP using a nephelometry-based assay. Sensitivity, specificity, and area under the curve (AUC) for beta-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 beta-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 beta-TP concentration in NS as a cutoff point for CSF leakage diagnosis with high sensibility and specificity. These results suggest that beta-TP analysis could be useful to check CSF leak resolution.