L BERNASCONI¹, T PÖTZL², S STEUER¹, A DELLWEG², F METTERNICH², AR HUBER<sup>1

1</sup>Institute of Laboratory Medicine, Kantonsspital Aarau AG, Aarau, Switzerland, ²Clinic of Otorhinolaryngology, Kantonsspital Aarau AG, Aarau, Switzerland

Cerebrospinal fluid (CSF) leakage is a rare condition which can potentially lead to the development of serious complications. In the last decade Beta-trace protein (B-TP) has been shown to be a valuable immunological biomarker which allows the prompt and non-invasive identification of CSF leakage. At our institution the measurement of B-TP has been included in the diagnostic work-up of CSF leakage since more than 10 years. According to our diagnostic algorithm, the presence of CSF in secretion is excluded when B-TP values are < 0.7 mg/L, whereas B-TP values ≥ 1.3 mg/L indicate the presence of CSF in secretion. B-TP values between 0.7 and 1.29 mg/L indicate the presence of CSF if the B-TP ratio (B-TP secretion /B-TP serum) is ≥ 2. This study aimed to validate this diagnostic algorithm using clinically defined nasal/ear secretions.

Methods: we performed a retrospective statistical analysis of three B-TP interpretation strategies using data of 236 samples originating from 121 patients with suspect CSF leakage received at our laboratory between 2004 and 2012.

Results and conclusion: the highest odd ratio was obtained when the proposed algorithm has been used for the interpretation of B-TP results, showing a sensitivity of 98.3% and a specificity of 96%. Positive and negative predictive values were 89.2% and 99.4% respectively. These data suggest that the proposed B-TP interpretation algorithm is a valuable tool for the diagnosis of CSF leakage in the clinical practice.