There are different ways to get a sample of spinal fluid. Lumbar puncture, commonly called a spinal tap, is the most common method of collecting Cerbral Spinal Fluid (CSF). CSF surrounds the brain and spinal cord, and acts like a cushion, protecting the brain and spine from injury. The fluid is normally clear. The test is usually performed in the following manner:

• The patient must lay on his or her side, with the knees pulled up toward the chest, and the chin tucked downward. Sometimes the test is done with the person sitting up, but bent over. After the back is cleaned, the doctor will inject a local numbing medicine into the lower spine. A spinal needle is inserted, usually into the lower back area. Once the needle is properly positioned, spinal fluid pressure is measured, and fluid is collected. The needle is removed, the area is cleaned, and a bandage is placed over the needle site. The patient is often asked to lie down for a short time after the test.

The patient (or guardian) must give permission to do the test.

The position may be uncomfortable, but it is extremely important that the patient stays in the bended position to avoid moving the needle and possibly injuring the spinal cord. The numbing medicine 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 tissue surrounding the spinal cord. This pain should stop in a few seconds. Overall, discomfort is minimal to moderate. The entire procedure usually takes about 30 minutes, but it may take longer. The actual pressure measurements and fluid collection only take a few minutes.

This test is done to measure pressures within the cerebrospinal fluid and to collect a sample of the fluid for further testing. CSF can be used to diagnose certain neurologic disorders, particularly infections (such as meningitis) and brain or spinal cord damage.

Risks of lumbar puncture include hypersensitivity to the medicines, discomfort during the test, a headache after the test, and bleeding into the spinal canal. There is an increased risk of bleeding in persons who take blood thinners. Brain herniation may occur if this test is done on a person with a mass in the brain (such as a tumor or abscess). This can result in brain damage or death. This test is not done if an exam or test reveals signs of a brain mass. Damage to the nerves in the spinal cord may occur, particularly if the person moves during the test.