A lumbar puncture (spinal tap) is performed in your lower back, in the lumbar region. During a lumbar puncture, a needle is inserted between two lumbar bones (vertebrae) to remove a sample of cerebrospinal fluid. This is the fluid that surrounds your brain and spinal cord to protect them from injury.
A lumbar puncture can help diagnose serious infections, such as meningitis; other disorders of the central nervous system, such as Guillain-Barre syndrome and multiple sclerosis; or cancers of the brain or spinal cord. Sometimes doctors use lumbar punctures to inject anesthetic medications or chemotherapy drugs into the cerebrospinal fluid.
During a lumbar puncture (spinal tap) procedure, you typically lie on your side with your knees drawn up to your chest. Then a needle is inserted into your spinal canal — in your lower back — to collect cerebrospinal fluid for testing.
A lumbar puncture may be done to:
Information gathered from a lumbar puncture can help diagnose:
Though lumbar punctures are generally recognized as safe, they do carry some risks. These include:
Post-lumbar puncture headache. Up to 25 percent of people who have undergone a lumbar puncture develop a headache afterward due to a leak of fluid into nearby tissues.
The headache typically starts several hours up to two days after the procedure and may be accompanied by nausea, vomiting and dizziness. The headaches are usually present when sitting or standing and resolve after lying down. Post-lumbar puncture headaches can last from a few hours to a week or more.
Brainstem herniation. Increased pressure within the skull (intracranial), due to a brain tumor or other space-occupying lesion, can lead to compression of the brainstem after a sample of cerebrospinal fluid is removed.
A computerized tomography (CT) scan or MRI prior to a lumbar puncture can be obtained to determine if there is evidence of a space-occupying lesion that results in increased intracranial pressure. This complication is rare.
Before your lumbar puncture, your doctor asks questions about your medical history, does a physical exam, and orders blood tests to check if you have any bleeding or clotting disorders. Your doctor may also recommend a CT scan or MRI to determine if you have any abnormal swelling in or around your brain.
Your doctor will give you specific instructions about food, drink and medications. You'll likely be asked not to eat or drink anything after midnight before your procedure.
Tell your doctor if you're taking blood-thinning or other anticoagulant medications. Examples include warfarin (Coumadin, Jantoven), clopidogrel (Plavix), and some over-the-counter pain relievers such as aspirin, ibuprofen (Advil, Motrin IB, others) or naproxen sodium (Aleve). Also, tell your doctor if you're allergic to any medications, such as numbing medications (local anesthetics).
A lumbar puncture is usually done in an outpatient facility or a hospital. Your doctor will talk to you about the potential risks, and any discomfort you might feel during the procedure.
If a child is having a lumbar puncture, a parent is usually allowed to stay in the room. Talk to your child's doctor about whether this will be possible.
You're asked to change into a hospital gown. There are a few possible positions for this test. Usually, you lie on your side with your knees drawn up to your chest, or you sit and lean forward on a stable surface. These positions flex your back, widening the spaces between your vertebrae and making it easier for your doctor to insert the needle.
For an infant or young child, someone will hold the child in position during the procedure.
Your back is washed with antiseptic soap or iodine and covered with a sterile sheet.
The procedure usually lasts about 45 minutes. Your doctor may suggest lying down after the procedure.
Sometimes, an ultrasound may be used as a guide during the procedure on infants and young children. The ultrasound can help prevent inserting the needle too far.
The spinal fluid samples are sent to a laboratory for analysis. Lab technicians check for a number of things when examining spinal fluid, including:
Lab results are combined with information obtained during the test, such as spinal fluid pressure, to help establish a possible diagnosis.
Your health care provider generally gives you the results within a few days, but it could take longer. Ask your doctor when he or she expects to receive the results of your test.
Write down questions that you want to ask your doctor. Don't hesitate to ask questions during your visit. Questions you may want to ask include: