A 32-year-old woman who sustained head trauma reports clear watery discharge from the right nostril, worse on leaning forward. When the fluid drips onto a white gauze piece, a central bloodstain is surrounded by a paler ring. Which biochemical finding would most specifically confirm that this fluid is cerebrospinal fluid?

• A Presence of beta-2 transferrin ✓
• B Elevated glucose content compared with serum
• C High sodium concentration
• D Presence of tau protein only

Explanation

Beta-2 transferrin, the desialylated isoform of transferrin found almost exclusively in cerebrospinal fluid, aqueous humour and perilymph, is the most specific marker for confirming CSF rhinorrhoea; nasal secretions and tears lack it. The double ring or halo sign on gauze is suggestive but not specific, since saline or tears mixed with blood produce a similar pattern. CSF glucose is actually lower than serum glucose, so elevated glucose argues against CSF, and sodium levels overlap broadly between secretions and CSF.

Reference: Bailey and Love's Short Practice of Surgery, 28th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.