Which statement best describes the diagnostic approach for meningitis?

• A. CT scan of the head with contrast
• B. Blood cultures only
• C. Lumbar puncture with CSF analysis
• D. EEG (electroencephalography)

Answer: (C)

Obtaining cerebrospinal fluid by lumbar puncture and analyzing it is how meningitis is diagnosed. The CSF directly surrounding the meninges reveals the infectious process and helps distinguish bacterial, viral, or fungal causes. In bacterial meningitis, the CSF typically shows a high white cell count with neutrophil predominance, elevated protein, and low glucose, and the Gram stain or culture often identifies the organism. In viral meningitis, the CSF usually has a lymphocytic predominance, with normal or mildly elevated protein and normal glucose, and PCR or viral testing can pinpoint the specific virus. Fungal meningitis tends to show its own distinct pattern and requires specific testing.

Blood cultures can be positive and useful for guiding therapy, but they do not by themselves confirm meningitis because the infection could be bloodstream-limited or CSF findings may be discordant. Imaging, such as a CT scan, isn’t used to diagnose meningitis itself; it’s reserved for situations where there’s concern for raised intracranial pressure or other contraindications to lumbar puncture before performing it.

So, the definitive diagnostic approach is lumbar puncture with CSF analysis, including cell count, protein and glucose, Gram stain/culture, and appropriate CNS pathogen testing.