Re-Assessing the Interpretation of Beta Trace Protein Levels in Middle Ear Fluid in the Assessment for Lateral Skull Base Cerebrospinal Fluid Leaks.

Hypothesis: Describe the range of values of BTP obtained in middle ear fluid samples and determine if the level of BTP is a reliable indicator of the presence of a cerebrospinal fluid middle ear effusion.

Background: Beta trace protein is a glycoprotein abundant in the CSF. Middle ear fluid samples are tested for the presence of BTP, which provides a numerical representation of the concentration of CSF. A middle ear fluid sample deemed to be positive for CSF has a BTP level of greater than 1.3 mg/L. However, this level is not specific to the middle ear, and there is a paucity of literature regarding interpretation of the BTP level when used in the evaluation for suspected lateral temporal bone CSF leaks.

Methods: Retrospective review of all middle and nasal fluid samples sent by otolaryngologists for beta trace protein testing in Western Australia over a 4-year period.

Results: A total of 168 patients had a middle ear fluid sample sent for BTP testing; these samples were obtained via tympanocentesis through an intact tympanic membrane with no other ear or temporal bone pathology. Ninety-six (96%) of the middle ear samples (172 of 178) had a BTP level greater than 1.3 mg/L, indicating a positive result and suggesting the presence of cerebrospinal fluid within the sample.

Conclusion: The BTP level of middle ear fluid aspirates should be viewed with caution and used in conjunction with radiological findings and clinical impressions in the formulation of a management plan in patients suspected of lateral skull base CSF leaks.