A procedure to collect cerebrospinal fluid (CSF). It involves inserting a needle between the third and fourth lumbar vertebrae in the back and extracting a sample of fluid. 

Parts of the Body Involved

The third and fourth lumbar vertebrae

Reasons for Procedure

  • Cerebrospinal fluid is withdrawn through a lumbar puncture and analyzed when the following conditions are suspected:
  • Meningitis (inflammation of the membranes that cover the brain and spinal cord)
  • Encephalitis (inflammation of the brain)
  • Guillain-Barré syndrome (inflammation of the nerves outside the brain and spinal cord)
  • Multiple sclerosis (chronic, disabling disease caused by inflammation, destruction, and scarring of the sheath that covers nerve fibers in the brain and spinal cord)
  • Any disorder affecting the nervous system
  • Central nervous system syphilis
  • Lymphoma, leukemia, or other cancers involving the brain or central nervous system
  • Certain forms of hydrocephalus (water on the brain)
  • Bleeding in the brain or spinal cord
  • A lumbar puncture may also be done in order to:
  • Administer dye for diagnostic imaging studies
  • Drain spinal fluid and lower pressure
  • Administer medications (such as chemotherapy or anesthesia)

Risk Factors for Complications during the Procedure

  • A local infection at the site where the needle would be inserted
  • Elevated pressure in the skull

What to Expect

Prior to Procedure

  • Possibly, a CT scan – a type of x-ray that uses a computer to make pictures of the inside of the body
  • Your back will be cleaned at the site where the needle will be inserted

During Procedure – Anesthesia

Anesthesia - Local

Description of the Procedure - You lie on your side with your knees drawn up to your abdomen. A needle is inserted into your spinal canal through your lower back. A sample of cerebrospinal fluid is withdrawn through the needle, and the pressure of the CSF is measured. If you experience discomfort during the procedure, the needle may need to be repositioned.

If you have a problem with the lower back that prevents you from assuming the curled position, the cerebrospinal fluid may be withdrawn from the top of the spine at the back of the neck, a procedure known as a cisternal puncture.

After Procedure - Cerebrospinal fluid is sent to a lab for analysis. You lie down for 10-15 minutes, and then you can leave, unless you have a severe headache.

How Long Will It Take? 30 minutes or more

Will It Hurt? Overall, discomfort is minimal to moderate. The anesthetic will sting when first injected, and there is usually a little pain when the needle is first inserted, but it should subside in a few seconds.

Possible Complications:

  • Local bleeding
  • Headache
  • Backache
  • Allergic reaction to the anesthetic

These complications are rare:

  • Herniation and death
  • Local infection
  • Pain or abnormal burning, pricking, or tingling sensations in your legs
  • Spinal, epidural, subdural, or subarachnoid hematomas (blood clots)
  • Inflammation of the arachnoid mater, a delicate membrane lining the nervous system
  • Temporary paralysis of a cranial nerve
  • Rupture of the soft, central portion of the intervertebral disk, called the nucleus pulposus
  • Delayed formation of intraspinal epidermoid tumors
  • Meningitis

Average Hospital Stay – None

Postoperative Care:

  • Drink extra fluids for the next 24 hours
  • Rest and remain quiet for the next 24 hours


Based on the pressure and contents of the CSF, a diagnosis can often be made. High pressure can indicate swelling, bleeding, a tumor, or hydrocephalus. The CSF is also analyzed for antibodies, bacteria, viruses, fungi, blood, cancer cells, excess protein, and white blood cells. Normal cerebrospinal fluid is clear and contains no blood. If there is blood or a yellowish color is present, it may indicate spinal cord obstruction or bleeding in the brain or spinal cord.

Call Your Doctor If Any of the Following Occurs

  • Severe headache or headache lasting for more than 24 hours
  • Signs of infection, including fever and chills
  • Redness, swelling, increasing pain, bleeding, or discharge from the site of the spinal tap
  • Tingling
  • Numbness or pain in your lower back and legs
  • Problems with urination

University of Iowa

The PDR Family Guide Encyclopedia of Medical Care. Three Rivers Press, 1997.

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