DefinitionA cerebrospinal fluid (CSF) smear is a microscopic examination of the clear fluid that moves in the space surrounding the spinal cord and brain. CSF protects the brain and spinal cord from injury.Alternative NamesSpinal fluid smear; Cerebrospinal fluid smearHow the test is performedA sample of CSF fluid is needed. This is usually done with a lumbar puncture. For information on how this procedure is performed, see spinal tap.The sample is sent to a laboratory, where a tiny amount is spread on a glass slide. A member of the laboratory team looks at the sample under a microscope. The smear shows the color of the fluid and the number and shape of cells present in the fluid. Other tests, such as a Gram stain, may be done to check for bacteria.How to prepare for the testFor information