A lumbar puncture is sometimes called a “spinal tap.” It’s a medical procedure that can involve collecting a sample of cerebrospinal fluid (CSF). CSF is the fluid that surrounds your spinal cord and brain. A laboratory can test it for signs of certain medical conditions and infections.

Your doctor may order a lumbar puncture for a few different reasons. They may use it to check for signs of certain medical conditions, such as:

  • meningitis
  • dementia
  • inflammation of the spinal cord (myelitis)
  • inflammation of the brain tissue (encephalitis)
  • demyelinating diseases, such as multiple sclerosis
  • autoimmune conditions
  • cancers that can affect your spinal cord, brain, or blood, such as leukemia
  • subarachnoid hemorrhage (bleeding around the brain)

In some cases, they may use a lumbar puncture to administer medication directly into your spinal canal. For example, they may use it to give you chemotherapy drugs.

A lumbar puncture can help your doctor accurately diagnose or rule out certain medical conditions, including some life threatening illnesses. The quicker they make a diagnosis, the sooner you can make choices about treatment. Some conditions, such as bacterial meningitis, can be fatal if not treated quickly.

A spinal tap procedure can also help your doctor give you some types of medication.

A lumbar puncture is generally considered safe, but it can involve some risks. About 10% of people who get a lumbar puncture develop a headache afterward. A headache might come on within a few hours or a few days.

In a 2020 study of 117 people who had a lumbar puncture, 13 experienced a headache after the procedure. Those were more likely to be younger and have a lower volume of cerebrospinal fluid (CSF) in their body.

Other potential risks include tenderness or pain in your lower back and bleeding near the puncture site. You may experience some pain and numbness that shoots down your legs. In rare cases, people experience brain herniation, which is the movement of brain tissue from its normal position in your skull. This is uncommon.

Tell your doctor about all of the medications you’re taking and ask them if you should stop taking any of them before a spinal tap procedure. For example, they may advise you to stop taking blood thinners, such as aspirin or warfarin.

Your doctor may also order a CT or MRI scan before your lumbar puncture. They can use it to check for signs of swelling around your brain or other problems.

Your doctor will conduct a lumbar puncture using a needle and syringe. They’ll collect a sample of your spinal fluid in a tube attached to the syringe. Then, they’ll send it to a laboratory for testing.

The procedure usually takes about 15 to 30 minutes. It usually includes the following steps:

  1. They’ll likely position you on your side or leaned forward.
  2. They’ll clean your back with an antiseptic solution to reduce your risk of infection and numb it with a local anesthetic.
  3. They’ll inject a hollow needle into your subarachnoid space to collect a sample of your CSF. You may feel some pressure at this point, but the procedure usually isn’t painful.
  4. After they remove the needle, they’ll clean and bandage the puncture site.

For a short period after the procedure, it’s likely they’ll monitor you for a headache, dizziness, or other side effects.

They’ll send the CSF sample to a lab for testing. Professionals in the lab may:

  • evaluate its appearance for cloudiness
  • check it for the presence of protein and glucose
  • measure the level of red and white blood cell levels it contains
  • check it for the presence of bacteria or viruses

It may take anywhere from a few hours to several days for them to analyze your sample. Your doctor can help you understand what the results mean. They’ll also advise you on any follow-up steps you should take.

Your long-term outlook will depend on your final diagnosis. Ask your doctor for more information about your specific condition, treatment plan, and long-term outlook.

How painful is a lumbar puncture?

A lumbar puncture is usually not painful. You may feel pressure when the needle goes in.

Is a lumbar puncture a serious procedure?

A spinal tap procedure is common. Side effects might include headache or low back swelling. Serious complications are rare.

Are you sedated for a lumbar puncture?

A doctor applies local anesthetic at the site of the lumbar puncture. You will be awake for the spinal tap procedure.

How long does a spinal tap procedure take?

A lumbar puncture takes about 15 to 30 minutes. However, after the procedure, your doctor will ask you to stay at the hospital or clinic for another few hours to ensure there are no complications.