During a lumbar puncture, a needle is carefully inserted into the spinal canal low in the back (lumbar area). Samples of CSF are collected. The samples are studied for color, blood cell counts, protein, glucose, and other substances. Some of the sample may be put into a container with a growth substance. This is called a culture. If any bacteria or fungi grow in the culture, an infection may be present. The pressure of the CSF also is measured during the procedure.

A lumbar puncture is done to:

• Find a cause for symptoms possibly caused by an infection (such as meningitis), inflammation, cancer, or bleeding in the area around the brain or spinal cord (such as subarachnoid hemorrhage).
• Diagnose certain diseases of the brain and spinal cord, such as multiple sclerosis or Guillain-Barré syndrome.
• Measure the pressure of cerebrospinal fluid (CSF) in the space surrounding the spinal cord. If the pressure is high, it may be causing certain symptoms.

A lumbar puncture may also be done to:

• Put anesthetics or medicines into the CSF. Medicines may be injected to treat leukemia and other types of cancer of the central nervous system.
• Put a dye in the CSF that makes the spinal cord and fluid clearer on X-ray pictures (myelogram). This may be done to see whether a disc or a cancer is bulging into the spinal canal.

In rare cases, a lumbar puncture may be used to lower the pressure in the brain caused by too much CSF.

Before you have a lumbar puncture, tell your doctor if you:

• Are taking any medicines. If you take medicines every day, ask your doctor whether you should take these medicines on the day of the lumbar puncture.
• Are allergic to any medicines, such as those used to numb the skin (anesthetics).
• Have had bleeding problems or take blood-thinners, such as aspirin, warfarin (Coumadin), or clopidogrel (Plavix).
• Are or might be pregnant.
• Take any herbal remedies. Some of these remedies may thin the blood.

You will empty your bladder before the procedure.

You will be asked to sign a consent form that says you understand the risks of the test and agree to have it done.

Talk to your doctor about any concerns you have regarding the need for the procedure, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

A lumbar puncture may be done in your doctor’s office, in an emergency room, or at your bedside in the hospital. It may also be done in the radiology department if fluoroscopy is used.

You will lie on a bed on your side with your knees drawn up toward your chest. Or you may sit on the edge of a chair or bed and lean forward over a table with your head and chest bent toward your knees. These positions help widen the spaces between the bones of the lower spine so that the needle can be inserted more easily. If fluoroscopy is used, you will lie on your stomach so the fluoroscopy machine can take pictures of your spine during the procedure.

Your doctor marks your lower back (lumbar area) with a pen where the puncture will occur. The area is cleaned with a special soap and draped with sterile towels. A numbing medicine (local anesthetic) is put in the skin.

Then a long, thin needle is put in the spinal canal. When the needle is in place, the solid central core of the needle (stylet) is removed. If the needle is in the right spot in the spinal canal, a small amount of cerebrospinal fluid (CSF) will drip from the end of the needle. If not, the stylet will be put back in and the needle will be moved in a little farther or at a different angle to get to the fluid. Your doctor may need to move to another area of your spine if it is hard to get to the spinal fluid.

When the needle is in the spinal canal, a device called a manometer is hooked to the needle to measure the pressure of the CSF. You may be asked to straighten your legs while you are lying down. Your doctor takes the pressure reading, called the opening pressure, and checks whether the fluid is clear, cloudy, or bloody. Several small samples of fluid are collected and sent to the lab for study.

A final pressure reading, called the closing pressure, may be taken after the fluid samples are done. The needle is taken out and the puncture site is cleaned and bandaged.

The doctor also may look into your eyes using a special lighted scope (ophthalmoscope) to see if the pressure is high.

The entire procedure takes about 30 minutes.

To lower your chance of getting a headache following a lumbar puncture, you may be told to lie flat in bed or with your head slightly raised for 1 to 4 hours. Since your brain makes new CSF all the time and replaces it 2 or 3 times a day, the small amount of fluid that is removed will be quickly replaced. You may be told to drink extra fluids after the procedure to help prevent or to reduce the severity of a headache.

Some people find it uncomfortable to lie curled up on their side. The soap may feel cold on your back. You will probably feel a brief pinch or sting when the numbing medicine is given. You may feel a brief pain when the spinal needle is inserted or repositioned.

During the procedure, the needle may touch one of your spinal nerves and cause a tingling feeling, like a light electrical shock, running down one of your legs.

You may feel tired and have a mild backache the day after the procedure. Some people have trouble sleeping for 1 to 2 days.

A lumbar puncture is generally a safe procedure. In some cases, a leak of cerebrospinal fluid (CSF) may develop after a lumbar puncture. Symptoms of this problem are a headache that does not go away after 1 to 2 days. A CSF leak can be treated with a blood “patch,” in which the person’s own blood is injected into the area where the leak is occurring in order to seal the leak.