A lumbar puncture (LP) is a procedure in which a small amount of the fluid that surrounds the brain and spinal cord, called the cerebrospinal fluid or CSF, is removed and examined. This test is sometimes also called a spinal tap.

In infants and children, the most common reason for doing a lumbar puncture is to look for an infection of the meninges, the membrane covering the brain and spinal cord. This infection inflames the meninges, and it is called meningitis. There are other reasons to do lumbar punctures, too: sometimes they are done to remove fluid and relieve pressure with certain types of headaches, sometimes they are performed to look for bleeding in the central nervous system, and sometimes they are done to place chemotherapy medications into the spinal fluid.

What Happens During a Lumbar Puncture?
First, the child is positioned so that the spaces between the vertebrae (bones of the spine) are as wide as possible. Infants and small children lie on their sides curled up with their knees under their chin, like the letter C. Teens may sit with their heads resting on a pillow placed on a table at waist level.

The skin covering the lower, or lumbar region, of the back is cleaned with an antibacterial solution and alcohol. The skin is then numbed with medication. Next, a small, hollow needle is inserted through the skin and then forward through the space between the vertebrae in the lower back until it enters the space that contains the spinal fluid. The spinal fluid drips out through the needle into a sequence of collection tubes and is sent to the lab for processing for a variety of tests. The pressure of the spinal fluid can also be measured as part of the test, which can provide important information. After the sample is collected (usually this takes a minute or so), the needle is withdrawn and a bandage is placed on the site.

The needle does not enter the spinal cord because the test is done in the lower back, below the level to which the spinal cord extends.