What is a Lumbar Puncture? Everything You Need to Know

A lumbar puncture, also known as a spinal tap, is a medical procedure that involves the insertion of a needle into the lower back to collect cerebrospinal fluid.

This fluid surrounds and protects the brain and spinal cord. A lumbar puncture is used to diagnose or treat a variety of conditions, such as meningitis, encephalitis, and Guillain-Barre syndrome. It can also be used to measure pressure in the brain or to remove the excess cerebrospinal fluid.

What is a lumbar puncture?

A lumbar puncture is a procedure that involves inserting a needle into the lower back to collect cerebrospinal fluid (CSF). A lumbar puncture entails a needle insertion into the space between two lower back bones (vertebrae) to remove a cerebrospinal fluid sample. This fluid surrounds and cushions the brain and spinal cord.

Why is it performed?

A lumbar puncture may be performed to:

  • Test for infections, such as meningitis or encephalitis
  • Test for bleeding around the brain
  • Test for certain cancers
  • Test for disorders of the nervous system, such as multiple sclerosis
  • Test for autoimmune disorders
  • Measure the pressure of the cerebrospinal fluid
  • Inject spinal anesthetics, chemotherapy medications, or other medicines into the spinal canal.
  • To obtain diagnostic pictures of the fluid’s flow, use dye (myelography) or radioactivity (cisternography) to inject into the cerebrospinal fluid.

What to expect before a lumbar puncture?

Before a lumbar puncture, your doctor will likely:

  • Ask about your medical history
  • Perform a physical exam
  • Explain the risks and benefits of the procedure
  • Answer any questions you have
  • You may be asked to sign a consent form

What happens during a lumbar puncture?

A lumbar puncture is usually performed in a hospital or doctor’s office. The procedure usually takes about 30- 40 minutes.

  • You will be asked to lie on your side with your knees pulled up toward your chest. This position helps to open up the space between the vertebrae.
  • Your doctor will clean the skin over the needle insertion site with a sterile solution.
  • A local anesthetic will be injected into the skin to numb the area. You may feel a brief sting when the needle is inserted.
  • A thin, hollow needle is inserted, and your doctor will remove a small amount of cerebrospinal fluid.
  • A bandage is used to cover the puncture wound after the needle has been removed. The fluid will be sent to a lab for testing.
  • You will be asked to lie still for a few minutes to prevent a headache that can sometimes occur after the procedure.

What happens after a lumbar puncture?

After a lumbar puncture:

  • You will be monitored for any complications.
  • You may be asked to stay in the hospital for a few hours.
  • Most people can go home on the same day.
  • You may have a headache after the procedure. This can be relieved by lying down and drinking plenty of fluids. Your doctor may also recommend pain medication or a blood patch. A blood patch is a procedure in which a small amount of your blood is injected into the area around the spinal canal to help seal the puncture.
  • You should avoid strenuous activity for 24 hours after the procedure. You should be able to resume your normal activities within a few days.


The results of a lumbar puncture are usually available within a few days. Your doctor will discuss the results with you and explain what they mean.

Lumbar puncture or spinal tap samples of fluid are sent to a laboratory for closer analysis. A few things lab technicians look for when examining the fluid are:

  • Spinal fluid is usually clear and colorless. If the hue is green, yellow, or pink, it might indicate an infection or bilirubin presence. A greenish spinal fluid could be an indication of an infection or a buildup of bilirubin.
  • Medical professionals believe that white blood cells in your spinal fluid may signify an infection or other condition if there are more than five white blood cells per microliter. Note that specific lab values can differ between medical facilities.
  • Total protein levels that are higher than 45 mg/dL may signify an infection or other inflammatory condition. Some proteins may give additional information about what is causing the inflammation. However, it’s important to keep in mind that different medical facilities use different methods for testing, so values may vary from place to place.
  • Cancer cells can be present in spinal fluid. Abnormal cells in spinal fluid may be a sign of cancer.
  • A high amount of sugar in the spinal fluid may result from diabetes, infections, tumors, or other problems.
  • The existence of bacteria, viruses, fungi, or other tiny organisms can sometimes mean you have an infection.

If the results are abnormal, further testing may be needed to determine the cause.

What are the risks of a lumbar puncture?

A lumbar puncture is generally a safe procedure. Complications are rare but can include:

  • Headache
  • Backpain
  • Bleeding
  • Infection
  • Nerve injury
  • Spinal fluid leak

Your doctor will discuss the risks of the procedure with you before it is performed.

What are the benefits of a lumbar puncture?

Lumbar punctures can be used to diagnose several conditions, including infections, bleeding disorders, cancers, and inflammatory diseases. They can also be used to measure pressure in the brain and spinal cord and to look for evidence of certain types of diseases.

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