This article waslast modified on September 12, 2018.

The lumbar puncture (also known as spinal tap) is usually performed while you are lying on your side in a curled up fetal position but may sometimes be performed in a sitting position. It is important that you remain still during the procedure.

Once you are in the correct position, your back is cleaned with an antiseptic and a local anesthetic is injected under the skin. When the area has become numb, a special needle is inserted through the skin, between two vertebrae, and into your spinal canal. An "opening" or initial pressure reading of the cerebrospinal fluid (CSF) is obtained. The healthcare practitioner then collects a small amount of CSF in multiple sterile vials. A "closing" pressure is obtained, the needle is withdrawn, and a sterile dressing and pressure are applied to the puncture site. You will then be asked to lie quietly in a flat position, without lifting your head, for one or more hours to avoid a potential post-test headache.

The lumbar puncture procedure usually takes less than half an hour. For most patients, it is a moderately uncomfortable procedure. The most common sensation is a feeling of pressure when the needle is introduced. Let your healthcare provider know if you experience a headache or any abnormal sensations, such as pain, numbness, or tingling in your legs, or pain at the puncture site.

The lumbar puncture is performed low in the back, well below the end of the spinal cord. There are spinal nerves in the location sampled, but they have room to move away from the needle. There is the potential for the needle to contact a small vein on the way in. This can cause a "traumatic tap," which just means that a small amount of blood may leak into one or more of the samples collected. While this is not ideal, it may happen a certain percentage of the time. The evaluation of your results will take this into account.