The central nervous system (CNS) is susceptible to bacterial, viral, and fu
ngal infections, and prion diseases. Examination of the cerebrospinal fluid
(CSF) is crucial in diagnosing these infections. Cerebrospinal tests may d
irectly identify an organism and its nucleic acid and surface constituents
by culture, polymerase chain reaction (PCR), or antigen detection. Alternat
ively, antibody to an organism may be identified in CSF by enzyme-linked im
munosorbent assay (ELISA), Western blot, or complement fixation assay. This
article discusses how these CSF tests are performed and addresses the sens
itivity and specificity of such tests for the diagnosis of selected CNS inf
ections.