What Is a Spinal Tap?

What to expect when undergoing this test

A lumbar puncture (LP), which is also called a spinal tap, is a common neurological test that's done to examine the cerebrospinal fluid (CSF)—the protective fluid that surrounds your brain and spinal cord. During the procedure, a needle is carefully inserted between the bones of the lumbar spine, which is in the lower back. A small amount of CSF is typically collected so it can be studied thoroughly in a lab. This procedure is used to help diagnose a wide variety of disorders, and it can be a treatment for certain conditions too.

what to expect during a spinal tap
Illustration by Emily Roberts, Verywell 

Purpose of the Test

Usually, an LP is performed to run diagnostic tests on the CSF. This helps with the diagnosis of certain diseases and with following the progression of some neurological disorders.

A spinal tap is commonly used to diagnose potentially life-threatening infections of the central nervous system. Diagnosing meningitis (inflammation of the membranes around the brain and spinal cord) is the most common reason for a lumbar puncture.

Meningitis causes a stiff neck, sudden high fever, severe headache, confusion, seizures, sleepiness, nausea, vomiting, and loss of appetite. Bacterial meningitis needs to be treated promptly to prevent serious complications.

Diagnosing a subarachnoid hemorrhage, which is bleeding in between the meninges, is another common reason for an LP. A computed tomography (CT) scan is normally performed first, but it may not always show the hemorrhage. When this is the case, a lumbar puncture is usually ordered next to look for blood. This condition can lead to brain damage or death and needs to be treated as soon as possible.

Other conditions that a lumbar puncture can help diagnose include:

This procedure may also be done to measure the CSF pressure around the spinal cord and brain, which helps with the diagnosis of pseudotumor cerebri, a condition that causes increased pressure around the brain. For treatment of this condition, CSF fluid is removed to decrease the pressure.

For people with problems such as severe scoliosis, arthritis, or obesity, an LP might require fluoroscopic guidance, which means that it is done while the doctor is using X-ray technology to visualize the spine. Some healthcare providers prefer to use fluoroscopic guidance with every patient to assist them in viewing the needle as it's placed.

Side Effects and Risks

The side effects and risks associated with a lumbar puncture include:

  • Headache: Up to one-third of people who get a lumbar puncture will later develop a spinal headache due to CSF leaking from the puncture site. The more leakage there is, the more severe the headache.
  • Back pain: You might feel mild and temporary aching in your back where the needle was placed.
  • Bleeding: There is a risk of bleeding from a lumbar puncture in the area that was punctured. Bleeding into the spinal canal is rare.
  • Infection: There's a slight risk of developing an infection in the site, but this rarely happens.
  • Tingling or numbness: Sometimes, the needle may brush against one of the peripheral nerves, which can cause temporary numbness or pain. If this happens, you may feel an uncomfortable but brief electric twinge that goes down your leg.
  • Brain compression or herniation: If there's a brain mass, such as an abscess or tumor, the pressure change caused by removing CSF can lead to dangerous shifting of brain tissue, which can cause compression or herniation of the brainstem. Usually, a CT scan or magnetic resonance imaging (MRI) scan of the brain is done prior to the procedure to rule out any mass.

Despite many people's fears, there is almost no chance of spinal cord damage or paralysis from an LP because the needle is inserted in the spinal canal well below where the spinal cord ends. The spine (backbone) is longer than the spinal cord, so there is plenty of space in your spinal canal that is not near your spinal cord.

Contraindications

Fluoroscopy is not recommended for women who are pregnant or think they could be pregnant. Special precautions may be taken or a different kind of test may be done instead.

Absolute Contraindications

  • Skin infection near the site of the lumbar puncture
  • Uncorrected bleeding disorders
  • Acute spinal cord trauma
  • Suspicion of increased intracranial pressure due to a mass in the brain

Before the Test

Sometimes an LP is done as an emergency procedure, such as when there is concern about meningitis or cancer metastasis. For conditions such as MS or chronic headaches, the procedure is usually scheduled in advance.

Before your procedure, your healthcare provider will order blood tests to make sure that your blood clots as it should and that your kidneys are functioning well. You may also have a CT scan or MRI beforehand.

Be sure to tell your healthcare provider if you're allergic to any medications, especially local or general anesthesia.

Timing

An LP normally takes around 15 minutes, and you'll be asked to lie down for another hour or two afterward to avoid a spinal headache.

Location

The procedure can be done on an outpatient basis at a hospital or clinic. If you're already in the hospital or emergency room, it may be performed at your bedside.

What to Wear

You'll be given a gown to wear for this procedure and you'll be asked to take off any jewelry, piercings, or accessories that could interfere with the test.

Food and Drink

Your healthcare provider will talk to you about food and drink restrictions before the procedure. If you will need to have general anesthesia, you will have to refrain from eating or drinking anything for several hours or more before the procedure.

In an emergency situation or if you will only need to have numbing medication placed in the skin around your back, these restrictions won't apply.

Medications

If you take blood-thinners like warfarin, clopidogrel, or heparin or nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin, ibuprofen, or naproxen, you may need to stop these several days beforehand to reduce the risk of bleeding.

Let your healthcare provider know about any other medications, supplements, or herbal remedies you're taking.

Cost and Health Insurance

The price of an LP can range from $400 to $4000 or more, depending on factors like where you'll have it and what tests will be run.

If you have health insurance, the cost should be covered, but you may want to check with your insurance provider to make sure and to find out about any co-pay or co-insurance for which you may be responsible.

What to Bring

If you are going in for a scheduled test, bring your insurance card and a form of identification with you.

If you are having this test as an outpatient, you will need someone to drive you home after the procedure, so be sure to bring along a friend or family member, or arrange for a service to pick you up when you're done.

During the Test

A neurologist or a radiologist will perform your lumbar puncture and there may be an assistant there as well.

Pre-Test

You may need to fill out a consent form before you have this procedure.

You'll need to change out of your clothes into a gown and then lie on your side on a table or your hospital bed in a fetal position with your knees tucked up toward your chest. If you will have your CSF pressure measured, this is done while you are lying on your side.

Alternatively, you may be asked to sit on the edge of the table or bed and bend forward, leaning on something stable with your back to the healthcare provider. These positions widen the area between your lumbar bones (vertebrae), allowing for easier access.

If your child is the one having the lumbar puncture, they may have intravenous (IV) sedation at this time.

Throughout the Test

The spinal tap takes about 15 minutes, plus recovery time.

  • Your lower back will be cleaned with a sterilizing agent such as iodine.
  • A local anesthetic, usually lidocaine, will be injected into your skin to numb the area. The injection of the numbing medication can cause a sharp poke and a slight burning sensation.
  • Once the skin on your back is numb, the neurologist or radiologist will insert a thin, hollow needle into your skin, between two of your vertebral bones, and advance the needle through the meninges and into the thecal sac. You will need to hold very still for this.
  • You may feel pressure or a twinge of pain or numbness down your leg when the needle is inserted. Sometimes the needle has to be repositioned to find the right spot.

The discomfort level during an LP can vary, but it's usually mild to moderate.

Once the needle is in place, what happens depends on why you're having the LP.

  • The doctor may measure the pressure of your CSF using a gauge called a manometer.
  • A small amount of your CSF may be collected in test tubes to be sent to the lab.
  • The doctor may measure the pressure of your CSF again after the fluid has been collected.
  • The needle is removed and a bandage is placed over the puncture site.

A similar procedure is used to inject chemotherapy, contrast dye for an imaging test, antibiotics, or anesthetics for surgery. When anesthetics are injected, it's called spinal anesthesia. During these procedures, the needle is not inserted into the meninges and remains above this protective tissue without puncturing it.

Post-Test

You may be asked to lie down flat for an hour or two after this procedure. You'll also be given fluids to help prevent a low-pressure headache.

If you're being discharged home, you'll be able to go home with your driver.

After the Test

You'll need to take it easy for the rest of the day, and it's a good idea to lie down if possible. Keep drinking water to make sure you stay hydrated. Your healthcare provider may give you more specific instructions.

Managing Side Effects

You may notice some back pain, numbness, or soreness that can feel like it's radiating down your legs for a few days. If it's bothersome, but mild, try over-the-counter pain relievers such as Tylenol (acetaminophen) to help relieve the discomfort.

Headaches can begin a few hours up to two days after your spinal tap. They're often minor, but sometimes they're accompanied by nausea, vomiting, dizziness, and a stiff neck.

If you experience a headache after a spinal tap, Tylenol (acetaminophen) or caffeine can help. Try lying down since being upright can make the pain worse.

Sometimes the headache is severe or persists for a few days to a week after the lumbar puncture—this may mean that the needle has left a hole in your thecal sac and fluid is still leaking out. In this case, a procedure called an epidural blood patch—in which your own blood is injected into the spinal canal—may relieve your headache as it slows down the leakage.

When to Call Your Healthcare Provider

  • If a severe headache persists a day or two despite treatment
  • If you experience numbness or tingling in your legs
  • If you have a high fever (over 100.4 F)
  • If there is bleeding or discharge from the injection site
  • If you are unable to urinate

Interpreting Results

Your test results may take several days or weeks to come back, depending on the type of test that's being done. If you are having a CSF culture, the results will take days or longer. Simple test results, such as a white blood cell (WBC) count or red blood cell (RBC) count, may be available within an hour.

The CSF can be tested for:

  • Color and clarity: CSF is normally clear with no color, like water. If it's pink, yellow, or cloudy, this may signify bleeding or inflammation in the brain.
  • Composition: An increased number of WBCs suggests infection or inflammation. A high number of RBCs is indicative of bleeding. Elevated levels of protein can also be an indicator of infection or an inflammatory disease like MS. A low level of glucose is most often due to a bacterial infection, and it can also occur with a tumor, inflammation, or other conditions.
  • Pathogens: CSF is checked for bacteria, viruses, and fungi.
  • Cancer cells: Abnormal cells in CSF can point to certain types of cancer.

When combined with other test results, as well as your symptoms, medical history, and physical exam, the information from an LP can help pinpoint a diagnosis.

In cases where you have an infection like meningitis or encephalitis, testing your CSF can tell your healthcare provider whether your infection is bacterial, viral, or fungal. This helps them know which treatment you need to take.

Follow-Up

You may need additional testing to figure out the specific cause of your symptoms. For possible MS, an LP alone can't diagnose this, so you may also have an MRI.

If you already had additional tests and the LP test result helped to confirm a specific diagnosis, your healthcare provider will discuss a treatment plan with you.

If your healthcare provider thinks you have leptomeningeal disease, a rare condition in which late-stage cancer has spread to the membranes around your brain and spinal cord, you will need at least three separate lumbar punctures to rule this out. Treatment may include radiation, chemotherapy, immunotherapy, and medications to help control your symptoms.

Be sure to talk to your healthcare provider about any questions or concerns you have regarding this test or your diagnosis.

A Word From Verywell

An LP, while uncomfortable, is not as bad as most people's fear. In most cases, the worst part is the pinch felt with the injection of the numbing medicine. While complications can occur, they are very infrequent. The benefits of obtaining the fluid for testing usually outweigh the risks and discomfort of the procedure.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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