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.