What Is a Spinal Tap?

What to expect when undergoing this test

Lumbar puncture: taking a sample of spinal fluid
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A lumbar puncture, or spinal tap, is a common neurological procedure in which a needle is inserted in between the bones of your lower back, called the lumbar region. Typically, a small amount of cerebrospinal fluid (CSF)—the protective fluid that surrounds your brain and spinal cord—is removed from your spinal canal so it can be studied more thoroughly in a lab. This procedure is used to help diagnose a wide variety of conditions, but has other uses as well.

Purpose of Test

Lumbar punctures are typically performed in order to run diagnostic tests on your CSF. This helps your doctor better diagnose a certain disease or understand how a disease you've already been diagnosed with is affecting you.

The procedure is commonly used in emergency departments to help find potentially life-threatening causes of symptoms. For instance, if you come in with symptoms like a stiff neck, sudden high fever, severe headache, confusion, seizures, sleepiness, nausea, vomiting, and loss of appetite and thirst, you will have a lumbar puncture to definitively diagnose or rule out meningitis, an infection that can be life-threatening. Testing for meningitis is actually the most common reason for a lumbar puncture since CSF is highly sensitive for this infection.

Another reason for an immediate lumbar puncture is a condition that causes bleeding in the subarachnoid space around your brain, known as a subarachnoid hemorrhage. A computed tomography (CT) scan is normally performed first, but it may not show the hemorrhage in some people. When this is the case, a lumbar puncture is usually ordered next to look for blood since 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 pressure of the CSF around your spinal cord and brain; to decrease the pressure in your spinal canal in conditions such as pseudotumor cerebri; or to inject medication like chemotherapy, contrast dye for an imaging test, antibiotics, or anesthetics for surgery. When anesthetics are injected, it's called spinal anesthesia.

For people with problems such as severe scoliosis, arthritis, or obesity, it may be too difficult for the neurologist to retrieve CSF at the bedside. In these situations, a lumbar puncture may be done using ultrasound or a live X-ray called fluoroscopy with the help of a radiologist. Some doctors prefer to use fluoroscopic guidance with every patient to assist them in viewing the needle as it's placed.

Risks and Contraindications

Despite many people's fears, there is almost no chance of cord damage or paralysis with a spinal tap because the needle is inserted well below where your spinal cord ends. Nerves branching off the spinal cord dangle down loosely through the thecal sac in what's called the cauda equina, or "horse's tail." This is where the CSF is located.

Risks

The risks associated with having a lumbar puncture include:

  • Headache: Up to one-third of people who get a lumbar puncture will later develop a headache due to CSF leaking from the puncture site or into the tissues around it. The more leakage there is, the more severe the headache.
  • Pain or numbness: After the spinal tap, you may feel temporary numbness or pain in your lower back and/or legs.
  • Bleeding: There is a risk of bleeding from a lumbar puncture, either in the area that was punctured or into the spinal canal, though the latter is rare.
  • Infection: As with any procedure that breaks your skin, there's always a slight risk of developing an infection in the site, but this rarely happens.
  • Puncture pain: Sometimes, the needle may brush against one of the nerves in the cauda equina, which can cause pain, but this only causes damage in about 1 out of 1,000 people and usually heals with time. More commonly, you may feel an uncomfortable but brief electric twinge that goes down your leg.
  • Brain compression or herniation: If you have a mass in your brain 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 your brainstem. A CT scan or magnetic resonance imaging (MRI) scan of your brain prior to your procedure can rule out any such mass.

    Depending on your specific medical condition, you may have other risks. Be sure to talk to your doctor about them.

    Contraindications

    If you have a fever or infection when you're scheduled to have your spinal tap, you'll most likely have to reschedule it. The exception to this is if your doctor ordered the test because you have a severe infection like encephalitis or meningitis. This usually happens in the hospital or emergency department.

    You may need to wait to have a lumbar puncture if you're on antibiotics, so be sure to let your doctor know if this is the case.

    Women who are pregnant or think they could be pregnant should talk to their doctors before having a spinal tap, especially if one with fluoroscopy is planned. Special precautions may be taken or a different kind of test may be done instead.

    Before the Test

    Once you've had a physical exam and medical history, if your situation isn't an emergency, your doctor will likely order blood tests before your lumbar puncture to make sure that your blood clots the way it should and that your kidneys are functioning well. You may also have a CT scan or MRI beforehand to check for swelling in or around your brain.

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

    Timing

    A lumbar puncture normally takes around 45 minutes to an hour, but often you're asked to lie down for another hour or two afterward.

    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 doctor will talk to you about food, drink, and medication restrictions before the procedure. You will likely need to refrain from eating or drinking anything for several hours or more before the spinal tap besides a very small amount of water to take your medications. However, in an emergency situation, these restrictions won't apply.

    If you take a blood-thinning medication like Coumadin (warfarin), Plavix (clopidogrel), or heparin, or if you're taking nonsteroidal anti-inflammatory drugs (NSAIDs) such as Motrin/Advil (ibuprofen), aspirin, or Aleve (naproxen), you may need to stop these a few days prior to the procedure to reduce the risk of bleeding. Let your doctor know about any other medications, supplements, or herbal remedies you're taking too.

    Cost and Health Insurance

    A lumbar puncture can range from $400 to $4000 or more, depending on factors like where you have it, what's included in the price, and what state you live in.

    If you have health insurance, this test should be covered, but you may want to check with your insurance provider or agent to make sure, as well as to find out if you need preauthorization before you have the test. You can also find out about any co-pay or co-insurance for which you may be responsible.

    If you don't have health insurance, consider calling around your area. Prices can vary greatly from facility to facility, but make sure you ask what the cost covers. In some cases, the price may reflect just the spinal tap alone without any diagnostic or doctor's fees. Also, ask about discounts for paying right away or any income-based discounts.

    What to Bring

    Since you will likely be lying down for an hour or two after your procedure, you may want to bring along a book or something else to do. You'll need someone to drive you home after your spinal tap, so bring along an adult friend or family member, or make sure they're ready to come pick you up when you're done. Bring your insurance card as well.

    During the Test

    A doctor, physician assistant, or nurse practitioner will perform your lumbar puncture and there may be an assistant there as well. If you have fluoroscopy or ultrasound, there may also be a radiologist or sonographer present.

    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. 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 practitioner. These positions widen the area between your lumbar bones (vertebrae), allowing for easier access.

    If your child is the one having the lumbar puncture, he or she may have intravenous (IV) sedation at this time, but most kids do just fine with the local anesthetic that's typically used.

    Throughout the Test

    The spinal tap itself usually takes about 45 minutes to an hour, plus recovery time.

    Your lower back will be cleaned with a sterilizing agent such as iodine and 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 slight burning sensation.

    Once your back is numb, the neurologist will insert a thin, hollow needle between two of your vertebrae into the thecal sac. You will need to hold very still for this. Sometimes the needle has to be repositioned to find the right spot. You may feel pressure or a twinge of pain or numbness down your leg when the needle is inserted.

    For infants and young children, an ultrasound machine may be used to help guide the doctor in placing the needle. A technician may help hold your child still as well, especially if he or she hasn't been sedated.

    Once the needle is in place, what happens depends on why you're having the lumbar puncture. The neurologist may measure the pressure of your CSF using a gauge called a manometer. After this, a small amount of your CSF may be collected in test tubes to be sent to the lab. The neurologist may measure the pressure of your CSF again after the fluid has been collected.

    Medication like antibiotics, chemotherapy, anesthesia, or dye may be injected if you're having the lumbar puncture for this purpose. If not, or once the substance is injected, the needle is removed and a bandage is placed over the site.

    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 replace the CSF that may have been collected. Both of these can help decrease your chance of developing a headache from the lumbar puncture.

    When you're discharged, you'll be able to go back to your hospital room if you're hospitalized or home with your driver.

    After the Test

    You'll need to take it easy for the rest of the day, but if you don't have a physically active job, you may be able to go back to work as long as you feel up to it. Be sure to ask your doctor ahead of time about this. Keep drinking water to make sure you stay hydrated. Your doctor 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 after the procedure for a few days. If it's bothersome, try over-the-counter pain relievers such as Tylenol (acetaminophen) to help relieve the discomfort.

    Headache: 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 do end up with a headache, Tylenol (acetaminophen) can help reduce the pain. Caffeine may also help, both to relieve pain and to help promote CSF production. Try lying down since being upright can make the pain worse.

    Sometimes the headache persists for a few days to a week after the lumbar puncture, which 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 thecal sac—may relieve your headache as it slows down the leakage.

    When to call your doctor: If your headache is severe or it doesn't go away within a day or two after treating it with pain relievers, caffeine, fluids, and lying down, give your doctor a call. You may just need to keep doing these at-home treatments for a time, but your doctor may want you to come in to get checked out.

    Call your doctor if you have any other abnormal after-effects from the procedure as well, such as numbness or tingling in your legs, fever, bleeding or fluid leakage from the injection site, inability to urinate, or anything else that's out of the ordinary.

    Interpreting Results

    Your test results may take several days or weeks to come back, depending on the type of test that's being done. For instance, if a culture is being done on your CSF, this is a more complex test that will take more time. In emergency cases, simple test results may be available much sooner.

    When cerebrospinal fluid is tested, a number of factors are considered, including:

    • Color and clarity: Cerebrospinal fluid is normally clear with no color, like water. If it's pink, yellow, or cloudy, this may signify bleeding or inflammation in your brain. Green fluid can be a sign of an infection.
    • Composition: The number of white blood cells CSF contains, as well as levels of components such as protein and glucose, are measured. An increased number of white blood cells suggests infection or inflammation. Elevated levels of protein can also be an indicator of infection or an inflammatory disease like MS; high levels of certain proteins may help diagnose Alzheimer's disease. A low level of glucose is most often due to a bacterial infection, but it can also occur with a tumor, inflammation, or other conditions. The ranges of what's normal for these tests may vary from laboratory to laboratory.
    • Pathogens: CSF is checked for bacteria, viruses, and fungi that could be causing an infection.
    • Cancer cells: Abnormal cells in CSF can point to certain types of cancer.

    If your lumbar puncture was performed on an outpatient basis to help diagnose your symptoms, your doctor will likely have you come in for a follow-up appointment to discuss your test results, as well as potential next steps. When combined with other test results, as well as your symptoms, medical history, and physical exam, the information from a lumbar puncture can help pinpoint a diagnosis.

    In cases where you have an infection like meningitis or encephalitis, testing your CSF can tell your doctor whether your infection is bacterial, viral, or fungal. This helps him or her know better how to treat you.

    Follow-Up

    You may need to have additional testing to figure out the specific cause of your symptoms. For instance, if your doctor is looking for multiple sclerosis, a lumbar puncture test alone can't diagnose this, so you may also have magnetic resonance imaging (MRI), blood tests, and electromyography to help establish a diagnosis.

    If you already had additional tests and the lumbar puncture test result helped to confirm a specific diagnosis, your doctor will discuss a treatment plan with you for that condition. For example, this is often the case with subarachnoid hemorrhage since a lumbar puncture may be the last test performed.

    If your doctor 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 diagnose or rule this out. Treatment for this condition may include radiation, chemotherapy, immunotherapy, and medications to help control your symptoms.

    Other Considerations

    Be sure to talk to your doctor about any questions or concerns you have regarding this test or your diagnosis. Open communication allows you to understand what's going on and helps you feel more in control of your health.

    If it's not an emergency situation and you want a second opinion on your test results and/or your diagnosis, talk to your doctor about getting your medical records. A second opinion doesn't mean that you don't trust your doctor and it can give you reassurance about your situation.

    A Word From Verywell

    A lumbar puncture, while uncomfortable, is not as bad as most patients fear. Usually 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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