What is the test of choice for meningitis?

• A. Brain MRI
• B. CSF analysis with LP
• C. Blood culture
• D. EEG

Answer: (B)

The essential approach to diagnosing meningitis is to analyze the cerebrospinal fluid obtained by a lumbar puncture. This yields direct information about what’s happening in the subarachnoid space and lets you identify the cause. CSF analysis provides cell counts and differential, opening pressure, glucose, and protein, plus Gram stain, culture, and often PCR. These results tell you not only that meningitis is present but also whether it’s bacterial, viral, or another etiology, which is crucial for choosing the right therapy. For example, bacterial meningitis typically shows neutrophilic pleocytosis, low glucose, and high protein, with Gram stain or culture often identifying the organism, whereas viral meningitis usually has a lymphocytic predominance with relatively normal glucose.

Imaging, like brain MRI, can help assess complications or rule out other conditions and may be used if there are signs that LP could be unsafe, but it cannot replace CSF analysis for diagnosing meningitis. Blood cultures can support the diagnosis and help identify causative organisms, but they do not definitively establish meningitis or its exact etiology in the same way CSF analysis does. EEG is not used to diagnose meningitis.

So, obtaining and analyzing CSF via lumbar puncture is the best test to confirm meningitis and guide treatment.