CSF smear is a microscopic examination of cerebrospinal fluid (CSF). CSF is a clear fluid that circulates in the space surrounding the spinal cord and brain.

CSF protects the brain and spinal cord from injury and carries products of neurosecretions (chemicals released by the neural tissue), nutrients, chemicals in the cells, and chemical changes in the cells.

The CSF is usually obtained through a lumbar puncture (spinal tap).

A small amount of the CSF is removed and sent to the lab. A smear involves spreading a thin sample on a glass slide, fixing (preserving) the sample, and staining. Often a Gram stain is done for bacteria. Less commonly, an acid-fast stain is done for tuberculosis and tuberculosis-like bacteria. Rarely, a fungal stain is done. It is then examined under a microscope.

Preparation is the same as for CSF collection.

You must sign a consent form. You must be prepared to remain in the hospital for at least the 6 to 8 hours that you must remain lying down.

The position may be uncomfortable, but it is imperative that the person remain in the curled position to avoid moving the needle and possibly injuring the spinal cord.

The scrub will feel cold and wet. The anesthetic will sting or burn when first injected. There will be a hard pressure sensation when the needle is inserted, and there is usually some brief pain when the needle goes through the meninges. This pain should stop in a few seconds.

Overall, discomfort is minimal to moderate. The entire procedure usually takes about 30 minutes but may take longer. The actual pressure measurements and fluid collection only takes a few minutes.

The examination under the microscope checks for microorganisms that may be causing an infection.

The absence of bacteria (a sterile fluid) is normal.

Bacteria or other microorganisms (tuberculosis, fungus, or viruses) are present, indicating bacterial meningitis or other infection.

Additional conditions under which the test may be performed include tertiary syphilis.

• Risks of lumbar puncture include:
  • Hypersensitivity (allergic reaction to the anesthetic)
  • Discomfort during the test
  • Headache after the test
  • Leaking of CSF after the test
  • Bleeding into the spinal canal
• Brain herniation (if performed on a person with increased intracranial pressure), potentially resulting in brain damage and/or death
• Damage to the spinal cord (particularly if the person moves during the test)

Not applicable.