Which finding indicates that drainage from the ear is cerebrospinal fluid?

Which finding indicates that drainage from the ear is cerebrospinal fluid?

• A. It is positive for glucose
• B. It is negative for glucose
• C. It is positive for protein
• D. It is negative for protein

Answer: (A)

The key idea is that cerebrospinal fluid has a measurable glucose level, reflecting its blood-derived composition. Draining from the ear that tests positive for glucose strongly suggests CSF leakage because most other ear secretions do not contain glucose. CSF glucose is typically about 60% of serum glucose, so its presence in the drainage is a reliable clue that the fluid is CSF. In contrast, relying on protein alone is less specific, since various ear secretions can have protein, and CSF protein levels can vary with conditions. Therefore, a positive glucose test in the ear drainage best indicates cerebrospinal fluid.

The key idea is that cerebrospinal fluid has a measurable glucose level, reflecting its blood-derived composition. Draining from the ear that tests positive for glucose strongly suggests CSF leakage because most other ear secretions do not contain glucose. CSF glucose is typically about 60% of serum glucose, so its presence in the drainage is a reliable clue that the fluid is CSF. In contrast, relying on protein alone is less specific, since various ear secretions can have protein, and CSF protein levels can vary with conditions. Therefore, a positive glucose test in the ear drainage best indicates cerebrospinal fluid.