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Lumbar puncture


A lumbar puncture is a common medical test. It is also called an “LP” and a “spinal tap.” In this test, a doctor or nurse practitioner uses a needle to take a small sample of fluid from around the spine. The fluid is called cerebrospinal fluid, or CSF. It surrounds and protects the brain and spinal cord. Testing the CSF can show if your child has a disease or infection.

Our bodies make CSF constantly, like blood. So your child’s body quickly replaces the small amount an LP takes.

Doctors can also do an LP to give chemotherapy. This is called “intrathecal (in-tra-THE-cal) chemotherapy.”

Getting ready for the test

About one (1) hour before the LP, a doctor or nurse practitioner might put numbing cream on the spot for the test. Usually, your child also gets medicine to help him sleep through the test. If your child will be awake, he might get an injection (shot) of liquid numbing medicine at the test spot.

Your child will be asked to lie on his side at the edge of the bed, with his knees curled up towards his stomach. Or he will sit on the side of bed, with his head resting on a table with a pillow on it. The doctor will feel your child’s lower back to find the right place to put the needle.

Next, the doctor puts on sterile gloves and cleans your child’s back with an antiseptic. This will feel cold if your child is awake. The doctor might put a plastic sheet called a “drape” over your child’s back, so just the test area shows.

The test

The doctor or nurse practitioner puts the needle in the right place on your child’s back. The needle is hollow, with a smaller needle inside. When the larger needle is in place, the doctor takes out the smaller one. This lets CSF go into the test tubes.

Getting a CSF sample usually takes 10 minutes or less. Then the doctor takes out the needle. Your child’s lumbar puncture is over. A nurse cleans the spot with alcohol and puts a bandage on it. The samples go to the St. Jude laboratory, where staff members study them under a microscope.

Will my child feel pain?

Probably not, or not very much. If your child is awake, he might feel a small pinch and some discomfort. But most people don’t think a lumbar puncture is painful.

When do we get the results?

Most results are available in 24 to 48 hours after a lumbar puncture. Your child’s doctor will talk about the results with you and your child.

After the test

The staff will probably ask your child to lie flat for about 30 minutes, and maybe longer if he gets a headache. He should also drink plenty of fluids to help prevent headaches.

You should take the bandage off your child’s back within 24 hours. If your child’s back is sore, the doctor might give medicine for this. Your child’s doctor can tell you which medicine your child should take.

Check your child’s back for any signs of infection after the test. These include:

  • Increased pain
  • Swelling
  • Redness
  • Bad odors

If you see any of these signs, call your child’s doctor.


If you have any questions about lumbar puncture, please talk to your child’s doctor or nurse by calling 901-595-3300. If you are inside the hospital, dial 0. If you are outside the Memphis area, dial toll-free 1-866-2STJUDE (1-866-278-5833) and press 0 after you are connected.


This document is not intended to take the place of the care and attention of your personal physician or other professional medical services. Our aim is to promote active participation in your care and treatment by providing information and education. Questions about individual health concerns or specific treatment options should be discussed with your physician.

St. Jude complies with health care-related federal civil rights laws and does not discriminate on the basis of race, color, national origin, age, disability, or sex.

ATTENTION: If you speak another language, assistance services, free of charge, are available to you. Call 1-866-278-5833 (TTY: 1-901-595-1040).

ATENCIÓN: si habla español, tiene a su disposición servicios gratuitos de asistencia lingüística. Llame al 1-866-278-5833 (TTY: 1-901-595-1040).

تنبيه: إذا كنت تتحدث باللغة العربية فيمكنك الاستعانة بخدمات المساعدة اللغوية المتوفرة لك مجانا. .يرجى الاتصال بالرقم. 5833-278-866-1  (الهاتف النصي: 1040-595-901-1).