What type of fluid does a spinal tap primarily analyze for diagnostic purposes?

A spinal tap, also known as a lumbar puncture, is primarily performed to collect and analyze cerebrospinal fluid (CSF). This fluid surrounds the brain and spinal cord, serving several essential functions, including protection, nutrient delivery, and waste removal.

When a healthcare provider performs a spinal tap, they insert a needle into the lumbar region of the spine to access the subarachnoid space, where the CSF is located. Analyzing this fluid can provide critical information about neurological conditions, infections (such as meningitis), bleeding (such as subarachnoid hemorrhage), and various inflammatory diseases.

In contrast, the other options do not pertain to a spinal tap. Synovial fluid is found in joint cavities and is analyzed for joint disorders. Interstitial fluid exists in the spaces between cells and is not typically collected for diagnostic purposes in the same way that CSF is. Plasma is the liquid component of blood and is analyzed in different contexts, such as for metabolic or hematological evaluations, rather than through a spinal tap procedure.