Spinal Tap

• What is it?
• Why is it done?
• How is it done?
• What are the limitations?
• What are the risks?

What is it?

Spinal tap refers to both a procedure and a lab test. Spinal fluid is extracted from the lower back and then tested to determine the spinal fluid pressure and contents.

Why is it done?

Doctors do a spinal tap to get a sample of cerebrospinal fluid (the fluid that surrounds the spinal cord). A spinal tap checks the pressure and content of the fluid. It is usually very clear. It contains proteins, sugar, and other substances that can be found in blood. It typically does not contain red blood cells or many white blood cells. Signs of problems include evidence of bleeding, an increase in white blood cells (infection fighting cells), an increase in protein levels, or inflammation. This could mean there is an infection, tumor, or hemorrhage around the brain or spinal cord.

How is it done?

To obtain the fluid sample, a needle will be inserted into the spinal canal in the low back. The needle is inserted through the back, usually between two of the vertebrae. You may be asked to sit and lean over or to lie on your side. Before the spinal needle is inserted, the skin will be cleansed with an antiseptic and numbed with lidocaine. The procedure usually takes only 10-15 minutes.

What are the limitations?

The spinal tap does not show much information about most types of back pain. It is not helpful if your doctor suspects you may have arthritis of the spine, a herniated disc, or spinal stenosis.