A 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.

The test is done to check for signs of infection in a sample of CSF.

A 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.

For information on how to prepare for the procedure to obtain the CSF sample, see spinal tap.

The laboratory test is painless and does not involve the patient.

For information on how it will feel to have a sample of CSF fluid removed, see spinal tap.