A lumbar puncture (LP) removes a small amount of cerebrospinal fluid (CSF) from the space around the spine for examination under a microscope. CSF is the fluid that surrounds the brain and spinal cord. A lumbar puncture is also called spinal tap and cerebrospinal fluid (CSF) collection.
Why an LP is done
An LP is done to:
- examine the CSF
- measure the pressure of CSF in the space surrounding the spinal cord
- remove CSF to decrease pressure in the space surrounding the spinal cord
- check for
- infection or inflammation (such as meningitis)
- bleeding (hemorrhage) in the area around the brain or spinal cord
- certain diseases of the brain and spinal cord, such as multiple sclerosis
- trauma to the central nervous system (CNS)
- check for cancer of the brain and spinal cord
- check for cancers that may involve the CNS, such as leukemia or lymphoma
- put anesthetic, drugs or contrast mediumcontrast mediumA substance used in some diagnostic procedures to help parts of the body show up better on x-rays or other imaging tests. into the CSF
- An anesthetic may be injected to freeze the spinal cord (spinal anesthetic).
- Chemotherapy drugs may be injected to treat leukemia and other types of cancer of the CNS (intrathecal chemotherapy).
- A contrast medium may be injected to make the spinal cord and CSF appear clearer on an x-ray.
- find out if cancer treatment is working
How an LP is done
An LP may be done in a clinic or hospital as an outpatient or inpatient procedure. The entire procedure usually takes 15–30 minutes (the actual CSF collection usually only takes a few minutes).
- A healthcare professional will help to get the person into the proper position and support that position throughout the procedure.
- An LP is usually done with the person lying on one side with their knees drawn up toward the chest. The chin is tucked into the chest, sort of like a letter C.
- It may also be done with the person sitting on the edge of a chair or bed and leaning forward onto some pillows with the back to the doctor.
- These positions help widen the spaces between the vertebrae (bones of the spine) so that the needle can be inserted more easily.
- The skin on the back is cleaned with an antiseptic solution and a sterile drape is placed around the area, leaving only a small area of skin showing.
- A local anesthetic is injected into the skin over the lower spine to numb the area. The person may feel a burning sensation as the anesthetic goes in.
- It is important for the person to lie or sit as still as possible during the procedure.
- A long, thin 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 is usually inserted between the 3rd and 4th or 4th and 5th lumbar vertebrae.
- The needle does not enter the spinal cord because the test is done in the lower back, below the level to which the spinal cord extends.
- Pressure or a stinging sensation is felt when the spinal needle is inserted.
- On rare occasions, the person may feel some tingling down one of their legs if the needle touches a nerve. This is temporary.
- A small amount of CSF is collected and sent to the laboratory to be examined.
- The needle is removed, the area cleaned and a small bandage is put on.
- To reduce the chance of headache after the procedure:
- The person often lies flat in bed or with their head slightly raised for about 1–2 hours.
- They should also drink extra fluids.
- Rest is encouraged for several hours after the test.
Potential side effects
Serious problems from a lumbar puncture are not common. Potential side effects may include:
- The person may have a mild backache for 1–2 days after an LP.
- leak of CSF
- A symptom of CSF leakage is a headache that does not go away after 1–2 days.
- The doctor may use a blood patch to stop the leak. The person’s own blood is injected into the area of the leak to seal it.
- irritation of a nerve
- This may cause temporary numbness and tingling.
- It usually heals on its own.
- infection of test site
- The area may be red and feel warmth.
- bleeding into the spinal canal
- side effects of general anesthetic
- sore throat
Call the doctor if:
- The person has a severe headache that lasts for more than 24 hours.
- There are signs of infection, such as fever or chills.
- There is redness, swelling, pain, bleeding or discharge from the area where the needle was inserted.
- The person describes feeling tingly or numbness in their lower back or legs.
- The person is having problems urinating.
What the results mean
The CSF is examined in the laboratory for:
- general appearance
- Normal CSF is clear and colourless.
- Cloudy CSF may indicate infection.
- Blood in the CSF may indicate bleeding in or around the brain or spinal cord.
- blood cell counts
- Normal CSF does not contain red blood cells (RBCs), but it may contain very few white blood cells (WBCs).
- A high WBC count may indicate infection.
- RBCs in the CSF may indicate bleeding or hemorrhage.
- Large amounts of protein may suggest infection, bleeding or disease.
- A low glucose level may indicate infection.
- cancer cells
- Cancer cells in CSF may indicate primary or metastatic brain tumours, leukemia or lymphoma.
Culturing and staining CSF helps identify the type of bacteria or other micro-organism that may be causing an infection.
Abnormal results may be a sign that the person has an injury or disease of the brain, spinal cord or nearby tissues.
If CSF pressure is high, it can cause certain neurological symptoms. Increased CSF pressure may be caused by swelling or bleeding in the brain, infection or other problems.
What happens if a change or abnormality is found
The doctor will decide whether further tests, procedures, follow-up care or additional treatment are needed.
Special considerations for children
Being prepared for a test or procedure can reduce anxiety, increase cooperation and help the child develop coping skills. Parents or caregivers can help prepare children by explaining to them what will happen, including what they will see, feel and hear during the test.
- Parents may be able to stay in the same room 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.
- Depending on the age of the child, sedation may be used. If sedation is used:
- The child may not be allowed to eat or drink several hours before the test.
- The child may have an IV put in.
- The child’s vital signs (heart rate, blood pressure, temperature and blood oxygen level) will be monitored throughout the procedure).
- A cream may be given to numb the area where the needle will be inserted.
- If the cream is to be applied at home beforehand, the doctor or nurse will show the parent where to put the cream.
The preparation you can provide for this test depends on the age and experience of the child. See the following for more age-specific information on helping children cope with tests and treatment.