Lumbar Puncture

A lumbar puncture, also called a spinal tap, is a procedure during which the fluid surrounding the spinal cord (called the cerebrospinal fluid or CSF) is withdrawn through a needle and examined in a laboratory.

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Why is a lumbar puncture procedure performed?

This procedure might be performed to:

  • Test CSF for diagnostic purposes
  • Monitor the disease process
  • Measure the pressure around the brain and spinal cord
  • Relieve pressure in the head
  • Give spinal anesthesia
  • Inject dye for an X-ray diagnostic test
  • Inject medicines (such as baclofen)

Testing the CSF can help in the diagnosis of disorders of the central nervous system that might involve the brain, spinal cord, or their coverings (meninges). The CSF contains glucose (sugar), proteins, and other substances found in the blood. When the CSF is examined in the laboratory, the following are evaluated:

  • The number and types of white blood cells
  • The level of glucose
  • The types and levels of proteins
  • The presence of bacteria, fungi, or abnormal cells

NOTE: Testing of the CSF might not be necessary if the spinal tap is done to inject a medicine (such as baclofen).

What to expect

Preparation for the procedure

  • Maintain your regular eating schedule. There are no dietary or fluid restrictions before the tests. Please eat and drink prior to your lumbar puncture, unless specifically told otherwise.
  • Ask your doctor for specific guidelines about discontinuing alcohol use, aspirin products, and anticoagulant medicines before the procedure.
  • Tell your doctor if you are allergic to Betadine® or Novocaine®.
  • Please make arrangements for transportation, as you might not want to drive immediately after the test.

Description of procedure

You will either: Lie on your side with your knees drawn as close to your chest as possible and your chin toward your chest. Or sit with your arms and head resting on a table. After your back is cleaned with an antiseptic, sterile cloths (called drapes) will be placed around the area.

A local anesthetic (numbing medicine) will be injected into the area on your back. You might feel a burning sensation until the medicine begins to work.

When the area is numb, a hollow needle is inserted in the lower back between the two lumbar vertebrae. This sometimes causes a pressure sensation.

The spinal canal is penetrated, and fluid is collected or medicine is injected. The spinal cord is not touched by the needle during the test. You might feel some discomfort or have a minor headache.

The needle is removed after the fluid is removed or the medicine has been injected. The area will be cleaned and covered with a small bandage.

You will lie on your back, side, or stomach for about an hour.

A blood sample will be taken from a vein in your arm and tested, along with the spinal fluid, in the laboratory.

NOTE: If the procedure was done to inject medicine, a blood sample might not be taken.

Side effects and risks of the procedure

  • Approximately 10 percent to 20 percent of people develop a spinal headache (one that worsens when sitting or standing).
  • The risk of infection is extremely low.
  • Occasionally, a small blood vessel is pierced causing bloody discharge. No treatment is needed.
  • The procedure is usually not painful but momentary twinges of pain might be felt if the needle brushes against nerve tissue.

Care after the procedure

  • Avoid strenuous or vigorous exercise for a day or so following the lumbar puncture.
  • If you have a headache, lie down as much as possible and drink plenty of caffeinated beverages.
  • Drink 2 ½ quarts of liquid the day of the lumbar puncture and the day after (regardless of headache).

When to call for help

Call your Mellen Center health care professional immediately if:

  • You notice any unusual drainage, including bloody discharge, at the puncture site.
  • You develop a fever
  • Your pain symptoms worsen
  • You develop nausea or vomiting

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