A lumbar puncture removes a small amount of cerebrospinal fluid (CSF) from the space around the spinal cord so that it can be looked at under a microscope. CSF is the fluid that surrounds and cushions the brain and spinal cord. A lumbar puncture is also called spinal tap and cerebrospinal fluid (CSF) collection.
Why a lumbar puncture is done
A lumbar puncture is done to:
- examine the CSF for cell counts, and for protein and glucose levels
- measure the pressure of CSF in the space around the spinal cord
- remove CSF to decrease pressure in the space around the spinal cord
- check for cancer of the brain and spinal cord
- check for cancers that may involve the central nervous system, such as leukemia or lymphoma
- check for infection or inflammation, bleeding around the brain or spinal cord and diseases of the brain and spinal cord
- put an anesthetic into the CSF to freeze the spinal cord (spinal anesthetic)
- inject chemotherapy drugs into the CSF to treat leukemia and other types of cancer of the central nervous system (intrathecal chemotherapy)
- put a contrast medium into the CSF to make the spinal cord and CSF appear clearer on an x-ray
How a lumbar puncture is done
A lumbar puncture may be done in a clinic or hospital. The entire procedure usually takes 15 to 30 minutes. (The actual CSF collection usually only takes a few minutes.) A healthcare professional will help you get into the proper position and will support you in that position throughout the procedure. It is important to lie or sit as still as possible during a lumbar puncture.
A lumbar puncture is usually done with you lying on one side with your knees drawn up toward your chest and your chin tucked into the chest, sort of like a letter C. It may also be done with you sitting up and leaning forward with your back to the doctor. These positions help widen the spaces between the bones of the spine (called the vertebrae) so that the needle can be inserted more easily.
The skin on your back is cleaned with an antiseptic solution. A local anesthetic to numb the area is injected into the skin over the lower spine. You may feel a burning sensation as the anesthetic goes in.
A spinal needle is inserted through the skin and then through the space between the vertebrae until it enters the space that contains the CSF. The needle does not enter the spinal cord because it is inserted in the lower back. The spinal cord doesn’t extend this far.
Most people feel pressure or a stinging sensation when the spinal needle is inserted. If the needle touches a nerve, you may also feel tingling down one of your legs. This is temporary.
A small amount of CSF is collected and sent to the lab to be looked at or more CSF is removed to lessen the pressure around the spinal cord. Chemotherapy or other medicine may be injected into the CSF if that is part of your treatment plan.
The needle is then removed, the area cleaned and a small bandage is put on.
To lessen the chance of headache after the procedure you will be told to lie on your back for about 1 to 2 hours. You will be encouraged to drink extra fluids and to rest for several hours after the test.
Serious problems from a lumbar puncture are not common. Potential side effects may include:
- nausea and vomiting
- irritation of a nerve may cause temporary numbness, tingling or pain down your legs
- infection where the needle was inserted
- bleeding into the spinal canal
Call the doctor if you have:
- a severe headache or a headache that lasts longer than a week
- signs of infection, such as fever or chills
- redness, swelling, pain, bleeding or discharge from the area where the needle was inserted
- tingling or numbness in your lower back or legs
What the results mean
The CSF, which is generally clear and colourless, is examined and tested in the laboratory.
- Cloudy CSF or a high white blood cell count in the CSF may mean you have an infection.
- Blood or red blood cells in the CSF may mean there is bleeding in or around the brain or spinal cord.
- Cancer cells in CSF may indicate primary or metastatic brain tumours, leukemia or lymphoma.
- Large amounts of protein may suggest infection, bleeding or disease.
- A low glucose level may mean you have an infection.
- Increased CSF pressure may be caused by swelling or bleeding in the brain, infection or other problems.
What happens if the result is abnormal?
Depending on the result, your doctor will decide if you need more tests, any treatment or follow-up care.
Special considerations for children
Preparing children before a test or procedure can lower anxiety, increase cooperation and help them develop coping skills. Preparation includes explaining to children what will happen during the test, including what they will see, feel, hear, taste or smell.
You may be able to be in the room with your child during the test.
Keeping still or holding a certain position for a long time can be stressful for a child. Rehearsing the position before the test can help the child feel more in control and understand what they need to do. A nurse may help children stay still by holding them in place during the procedure.
Depending on the age of the child, sedation may be used. If sedation is used, your child may not be allowed to eat or drink several hours before the test and may have an IV.
A cream may be given to numb the area where the needle will be inserted. If you need to put the cream on at home beforehand, the doctor or nurse will show you what to do.
Preparing a child for a lumbar puncture depends on the age and experience of the child. Find out more about helping your child cope with tests and treatments.