What Is a Spinal Tap?
One test for epilepsy is a spinal tap -- also called a lumbar puncture -- that is performed by withdrawing fluid surrounding the spinal cord (called the cerebrospinal fluid or CSF) and examining it in a lab.
Why Is a Spinal Tap Performed?
This procedure may be performed to:
- Measure the pressure around the brain and spinal cord
- Relieve pressure in the head
- Give spinal anesthesia
- Inject dye for an X-ray test
- Inject medications (such as haclofen)
Testing the CSF can help in the diagnosis of disorders of the central nervous system that may involve the brain, spinal cord, or their coverings (called the meninges). The CSF contains glucose (sugar), proteins, and other substances found in the blood. When the CSF is examined in the lab, 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 may not be necessary if the spinal tap procedure is done to inject a drug.
What to Expect From a Spinal Tap
Preparation for a spinal tap
- Maintain your regular eating schedule. There are no dietary or fluid restrictions before the test.
- Ask your doctor for specific guidelines about discontinuing alcohol use, aspirin products, and blood-thinning drugs before the procedure.
- Tell your doctor if you are allergic to latex or any medications.
- Make arrangements for transportation, as you should not drive immediately after the test.
Description of a spinal tap
During a spinal tap, 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 cleaning your back with an antiseptic, sterile cloths (called drapes) will be placed around the area. A local anesthetic (pain-relieving medication) will be injected into the area on your back. You may feel a slight burning sensation. When the area is numb, a hollow needle is inserted in the lower back between two lumbar vertebrae. This sometimes causes pressure. The spinal canal is penetrated and fluid is collected or medication is injected. The spinal cord is not touched by the needle during the test. You may feel some discomfort or have a minor headache. The needle is removed after the medication has been injected or fluid is removed. The area will be covered with a small bandage. A blood sample will be taken from a vein in your arm and tested, along with the spinal fluid, in the lab. If the spinal tap was done to inject medication, a blood sample may not be taken.
Side effects and risks of a spinal tap
- Approximately 10% to 20% 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 may be felt if the needle brushes against nerve tissue.
Care after a spinal tap
- Once a spinal tap is completed, you will be instructed to lie flat. The time spent flat after the tap will vary depending on why you received the procedure.
- Avoid strenuous or vigorous exercise for a day or so following the lumbar puncture.
- If you have a headache, lay down as much as possible and drink plenty of fluids. Contact your health care provider if the headache persists.
- Drink 2 1/2 quarts of liquid the day of the lumbar puncture and the day after (regardless of headache).
When to Contact the Doctor After a Spinal Tap
After a spinal tap, call your local doctor immediately if:
- You notice any unusual drainage, including bloody discharge, at the puncture site
- You develop a fever
- Your headache persists
- Your pain symptoms worsen
After the Spinal Tap
You will be monitored for a few hours after a spinal tap procedure. At that time, the nurse will discuss post-procedure instructions with you. You will be provided with a written form of these instructions to follow at home.
The results of your spinal tap will be discussed within 24 hours with the doctor who ordered it, although some tests may take as long a week to be completed.