What is a lumbar puncture?
A lumbar puncture (LP) or spinal tap may be done to diagnose or treat a condition. For this procedure, your healthcare provider inserts a hollow needle into the space surrounding the spinal column (subarachnoid space) in the lower back to withdraw some cerebrospinal fluid (CSF) or inject medicine.
CSF is a clear fluid that bathes and cushions the brain and spinal cord. It is continuously made and reabsorbed in the brain. CSF is made up of cells, water, proteins, sugars, and other substances that are essential to maintain balance in the nervous system.
Why might I need a lumbar puncture?
A lumbar puncture may be done for many reasons. The most common reason is to remove a small amount of CSF for testing. This can help in the diagnosis of various disorders. The fluid is tested for red and white blood cells, protein, and glucose (sugar). The clarity and color of the fluid are also checked. It is tested to see whether bacteria, viruses, or abnormal cells are present. Excess CSF may also be removed in people who have an overproduction or decreased absorption of the fluid.
A lumbar puncture procedure may be helpful in diagnosing many diseases and disorders, including:
- Meningitis. An inflammation of the membrane covering the brain and spinal cord. The inflammation is usually the result of a viral, bacterial, or fungal infection.
- Encephalitis. An inflammation of the brain that is usually caused by a virus.
- Certain cancers involving the brain and spinal cord.
- Bleeding in the area between the brain and the tissues that cover it (subarachnoid space).
- Reye syndrome. A sometimes fatal disease that causes severe problems with the brain and other organs. The exact cause of the disease is not known. But it has been linked to giving aspirin to children. It is now advised not to give aspirin to children during illnesses, unless prescribed by your child's healthcare provider.
- Myelitis. An inflammation of the spinal cord or bone marrow.
- Neurosyphilis. A stage of syphilis during which the bacteria invades the central nervous system.
- Guillain-Barré syndrome. A disorder in which the body's immune system attacks part of the nervous system.
- Demyelinating diseases. Diseases that attack the protective coating that surrounds certain nerve fibers, such as multiple sclerosis or acute demyelination polyneuropathy.
- Headaches of unknown cause. After evaluation and head imaging if needed, a lumbar puncture may be done to diagnose certain inflammatory conditions that can result in a headache.
- Pseudotumor cerebri (also called idiopathic intracranial hypertension, or IIH). In this condition, pressure within the subarachnoid space is elevated for reasons that are not clear. A lumbar puncture is only done in this condition after evaluation and head imaging.
- Normal pressure hydrocephalus. A rare condition affecting mainly older people in which there is a triad of loss of urinary control, memory problems, and an unsteady gait. A lumbar puncture is done to see if the pressure of the CSF is elevated or not.
In addition, a lumbar puncture may be used to measure the pressure of the CSF. The healthcare provider uses a special tube (called a manometer) to measure the pressure during a lumbar puncture.
Finally, a lumbar puncture may be done to inject medicine directly into the spinal cord. These include:
- Spinal anesthetics before a surgical procedure
- Contrast dye for X-ray studies, such as myelography
- Chemotherapy drugs used to treat cancer
Your healthcare provider may have other reasons to recommend a lumbar puncture.
What are the risks of a lumbar puncture?
Because this procedure involves the spinal cord and brain, the following complications may occur:
- A small amount of CSF can leak from the needle insertion site. This can cause headaches after the procedure. If the leak continues, your headache can be severe.
- You may have a slight risk of infection because the needle breaks the skin’s surface, providing a possible way for bacteria to enter the body.
- You may have temporary pain or numbness of your legs or lower back pain.
- Bleeding may occur in the spinal canal.
You may have other risks, depending on your specific health condition. Talk about any concerns with your healthcare provider before the procedure.
How do I get ready for a lumbar puncture?
Check with your healthcare provider about what you should do before the procedure. Below is a list of common steps that you may be asked to do:
- Your healthcare provider will explain the procedure to you. Ask your provider if you have any questions about the procedure.
- You will be asked to sign a consent form that gives permission to do the procedure. Read the form carefully and ask questions if something is not clear.
- Generally, you won’t need to fast before a lumbar puncture unless a sedative is prescribed. Follow your healthcare provider's instructions.
- Tell your provider if you are pregnant or think you may be.
- Tell your provider about any medicines (prescribed and over-the-counter) and herbal supplements you take.
- Tell your provider if you have a history of seizures or if you are taking any prescribed medicines for seizures.
- Tell your provider if you have had any back surgery.
- Tell your provider if you have a history of bleeding disorders or if you are taking any anticoagulant (blood-thinning) medicines, aspirin, or other medicines that affect blood clotting. It may be necessary for you to stop these medicines before the procedure.
- If the procedure is done on an outpatient basis, you may be asked to stay in the hospital for several hours after the procedure. Plan to have another person drive you home.
- Based on your medical condition, your provider may request other specific preparation.
What happens during a lumbar puncture?
A lumbar puncture procedure may be done on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your healthcare's practices. Some healthcare providers may prefer to do this procedure at the bedside or may opt to have it done using a type of live X-ray called fluoroscopic guidance.
Generally, a lumbar puncture follows this process:
- You will remove any clothing, jewelry, or other objects that may interfere with the procedure.
- You will be given a gown to wear.
- You will be reminded to empty your bladder prior to the start of the procedure.
- During the lumbar puncture you may lie on the exam table on your side with your chin tucked to your chest and knees tucked to your abdomen. Or you may sit on the edge of an exam table with your arms draped over a table positioned in front of you. In either position the back is arched, which helps to widen the spaces between your vertebrae.
- Your back will be cleansed with an antiseptic solution and draped with sterile towels. The healthcare provider will wear sterile gloves during the procedure.
- The provider will numb the skin by injecting a local anesthetic. This injection may sting for a few seconds, but makes the lumbar puncture less painful.
- The hollow needle will be inserted through the numbed skin and into the space where the CSF is located. You will feel some pressure while the needle is inserted. You must remain absolutely still during the insertion of the needle.
- The CSF will begin to drip out of the needle and a small amount, about 1 tablespoon, will be collected into test tubes.
- If the provider needs to inject medicine into the spinal canal, it will be given through the same needle after the CSF is collected.
- When the procedure is done, the needle will be removed and a bandage will be placed over the injection site. The test tubes will be taken to the lab for testing.
- Tell the healthcare provider if you feel any numbness, tingling, headache, or lightheadedness during the procedure.
You may have discomfort during a lumbar puncture. Your healthcare providers will use all possible comfort measures and complete the procedure as quickly as possible to minimize any discomfort or pain.
What happens after a lumbar puncture?
You usually will be asked to lie flat for about 1 hour after the lumbar puncture is completed. This helps reduce the incidence of a headache. You will be allowed to roll from side to side as long as your head is not elevated. If you need to urinate, you may need to do so in a bedpan or urinal during the time that you need to stay flat.
You will be asked to drink extra fluids to rehydrate after the procedure. This replaces the CSF that was withdrawn during the spinal tap and reduces the chance of developing a headache.
After recovery, you may be taken to your hospital room or discharged to your home. If you go home, usually your healthcare provider will advise you to only engage in very light activity the rest of the day.
Once you are at home, notify your provider of any abnormalities, such as:
- Numbness and tingling of the legs
- Drainage of blood or pain at the injection site
- Inability to urinate
If the headaches persist for more than a few hours after the procedure, or when you change positions, contact your provider.
You may be instructed to limit your activity for 24 hours following the procedure. Generally, if no complications occur, you may return to your normal diet and activities.
Your healthcare provider may give you other specific instructions about what you should do after a lumbar puncture.
Before you agree to the test or the procedure make sure you know:
- The name of the test or procedure
- The reason you are having the test or procedure
- What results to expect and what they mean
- The risks and benefits of the test or procedure
- What the possible side effects or complications are
- When and where you are to have the test or procedure
- Who will do the test or procedure and what that person’s qualifications are
- What would happen if you did not have the test or procedure
- Any alternative tests or procedures to think about
- When and how you will get the results
- Who to call after the test or procedure if you have questions or problems
- How much you will have to pay for the test or procedure