A spinal tap can be used to sample CSF for detecting meningitis and other conditions. Which statement about spinal taps is true?

• A. It samples CSF to detect meningitis and other conditions
• B. It images the brain
• C. It measures brain electrical activity
• D. It replaces CSF with air

Answer: (A)

Spinal taps involve inserting a needle into the lower back to access the cerebrospinal fluid in the subarachnoid space and collect a sample for analysis. The CSF sample is then examined for signs of infection or other problems—things like white blood cell count, glucose and protein levels, Gram stain, cultures, and sometimes PCR to identify pathogens. This is how meningitis is detected and how doctors look for other CNS conditions that affect the CSF, such as subarachnoid hemorrhage or inflammatory disorders. The procedure can also provide opening pressure, which helps assess intracranial pressure.

It doesn’t image the brain—imaging requires MRI or CT scans. It doesn’t measure brain electrical activity—EEG performs that. It also isn’t about replacing CSF with air; the purpose is to collect CSF for testing, not to swap it with air.