How is CSF glucose interpreted in meningitis?

• A. CSF glucose is typically high in bacterial meningitis.
• B. CSF glucose is unaffected by meningitis.
• C. CSF glucose is always normal in meningitis.
• D. CSF glucose is typically low in bacterial meningitis and may be normal or slightly decreased in viral meningitis; compare to serum glucose.

Answer: (D)

CSF glucose reflects the balance between glucose entering the CSF from blood and glucose consumed by cells within the CSF and inflammatory exudates. In meningitis, the inflammatory response and bacterial metabolism consume more glucose in the CSF, and injury to the blood-CSF barrier can reduce glucose transport, so bacterial meningitis often causes a drop in CSF glucose. In contrast, viral meningitis typically has less glucose consumption and milder barrier disruption, so CSF glucose is usually normal or only slightly decreased and remains close to the serum level. It’s helpful to compare CSF glucose to serum glucose, since normal CSF glucose is about 60% of serum glucose; a low CSF glucose with a low CSF/serum ratio supports bacterial meningitis, whereas a normal or near-normal CSF glucose favors viral meningitis.