What Is a Spinal Tap/Lumbar Puncture?

A lumbar puncture, or spinal tap, is a medical test that involves collecting a small sample of cerebrospinal fluid (CSF) for examination. This clear, colorless liquid helps "cushion" the brain and spinal cord, or central nervous system.

Doctors use the fluid sample to look for signs of possible infections or other illnesses.

Why Are Spinal Taps Done?

The central nervous system is made up of the brain and spinal cord. It's the "command center" for the body. The spinal cord sends signals to and from the brain, and the brain interprets them. Cerebrospinal fluid constantly flows around the central nervous system while protecting it.

A CSF sample can provide a lot of important information about a person's health. So a spinal tap can help doctors find or rule out many diseases or conditions.

Most often, doctors order a spinal tap to see if a child has meningitis (infection of the covering of the brain and spinal cord). A spinal tap also can help them look for other conditions that affect the nervous system.

Spinal taps also can be used to add medicine, anesthesia, or dye (for specialized X-rays) directly into the cerebrospinal fluid. Occasionally, they're done to help relieve pressure in the brain when a condition causes the body to make too much CSF.

What Happens Before a Spinal Tap?

If your child needs a spinal tap, you'll have the chance to ask questions first. Then, you'll be asked to sign an informed consent form. This states that you understand the procedure and its risks, and give your permission for it.

Many spinal taps are done in the emergency department.

Some parents choose to be in the room with their child during the spinal tap, while others are more comfortable in a waiting area. You can ask the doctor if it is OK for you to stay.

What Happens During a Spinal Tap?

A spinal tap is a common procedure that takes about 30 minutes or less.

The spinal cord extends from the lower part of the brain down to the upper lumbar area. A spinal tap is done in the lower lumbar area, below the point where the spinal cord ends. So, the risk of harming the spinal cord is avoided.

A spinal tap is not surgery. No stitches or long recovery time are needed. Someone getting a spinal tap might be awake, or may get medicine to help them relax or sleep during the test. The medicine can be given by mouth, into the nose, or through an IV.

Patients are positioned with their back curved so the spaces between the  vertebrae  are as wide as possible. This makes it easier for the doctor to insert the needle.

Older children may be asked to either sit on an exam table while leaning over with their head on a pillow or lie on their side. Infants and younger children are placed on their sides with their knees near their chin. They will be held in this position during the test.

Then, the doctor cleans the area where the spinal needle will go in, and might put a cream on the skin before using a tiny needle to numb the area. The cream eases the discomfort of the needle, although the injection may still burn a little.

The spinal needle used for the "tap" is thin with a hollow core. Inside the core is a "stylet," another type of thin needle that acts kind of like a plug. When the patient is in position, the doctor carefully inserts the spinal needle between two vertebrae. When the needle reaches an area called the spinal canal, the doctor slowly pulls out the stylet, which lets the cerebrospinal fluid drip into the collection tubes. This takes only a few minutes.

Then, the doctor puts the stylet back into the needle, withdraws the needle, and puts a bandage on the site. The sample goes to a lab for testing.

What Happens After a Spinal Tap?

If you were not in the room with your child during the test, you can come in after the sample is collected. The doctor might want your child to lie down on their back for an hour or so after the test.

Some results are ready within 30 to 60 minutes. But bacterial cultures done to look for specific bacteria go to the lab. These results are usually ready in about 48 to 72 hours. Sometimes, the doctor will start antibiotic treatment while waiting for the culture results.

Lab technicians look for several things when examining the cerebrospinal fluid sample, including:

• General appearance: CSF should be clear and colorless like water. Cloudy spinal fluid or any blood in the sample may indicate an infection or other problem.
• Cell count: This includes the number and type of blood cells. Too many white blood cells can indicate an infection.
• Protein: Large amounts of protein in the CSF can suggest an infection or other diseases.
• Glucose: In bacterial infections of the central nervous system, the glucose level of the CSF is sometimes low.

Lab technicians also do a Gram stain and culture on the sample to look for bacteria.

What Are the Risks of a Spinal Tap?

A spinal tap is a safe procedure with few risks. Rarely, complications can include:

• Headache: After a lumbar puncture, a patient may have to lie down for a few hours and drink plenty of liquids, which can help prevent a headache. Babies do not need to do this. If your child gets a headache, acetaminophen or another non-aspirin type of pain reliever usually helps. If a headache lasts for more than 2 days, call your doctor.
• Infection: In rare cases, infection can happen if bacteria get into the skin when the puncture is done. This is very rare because doctors always clean the skin and use sterile techniques to do the test.
• Bleeding: If a small blood vessel under the skin is nicked during the spinal tap, there may be some bleeding.

When your child is having any kind of procedure, it's understandable to be a little uneasy. But it helps to know that spinal taps are quick, common tests and that complications are rare. If you have any questions or concerns, talk with your doctor.