Three weeks after endoscopic ethmoidectomy, a patient reports clear watery nasal discharge that increases on bending forward. Fluid collected from the nose is sent for analysis. Which laboratory finding confirms that the discharge is cerebrospinal fluid rather than allergic rhinorrhoea?

• A High protein content with absence of albumin
• B Elevated glucose concentration above 60 mg/dL alone
• C Presence of tau-transferrin (beta-2 transferrin) on electrophoresis ✓
• D Positive halo sign on filter paper testing

Explanation

Beta-2 transferrin (tau-transferrin) is found only in cerebrospinal fluid, perilymph and aqueous humour, so electrophoretic detection confirms a CSF leak with near-total specificity. Glucose testing alone is unreliable because nasal secretions and tears contain enough glucose to cause false positives. The double ring or halo sign on filter paper is suggestive but nonspecific and cannot replace biochemical confirmation.

Reference: Scott-Brown's Otorhinolaryngology and Head and Neck Surgery, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.