Which diagnostic test involves sampling cerebrospinal fluid for laboratory analysis?

• A. Spinal Tap
• B. Nerve Conduction Velocity Test
• C. EMG Test
• D. CT Scan

Answer: (A)

Sampling cerebrospinal fluid for laboratory analysis is done with a spinal tap, also called a lumbar puncture. This procedure uses a needle inserted into the lower back to reach the subarachnoid space and collect CSF for testing. Analyzing the fluid helps diagnose conditions such as meningitis, intracranial hemorrhage, certain cancers, or other central nervous system problems by checking cell counts, protein and glucose levels, cultures, cytology, or PCR results. The test is chosen when signs point to CNS infection or pathology and the information will guide treatment. It’s performed with sterile technique, often with the patient on their side or sitting, and local anesthesia; opening pressure can also be measured. Risks include post-procedure headaches, infection, or bleeding, so clinicians assess contraindications like signs of raised intracranial pressure before proceeding. The other listed tests do not involve sampling CSF: nerve conduction velocity and EMG assess nerve and muscle electrical activity, and CT scan is an imaging study.