Cerebrospinal fluid (CSF) collection is a test to look at the fluid that surrounds the brain and spinal cord. Cerebrospinal fluid acts as a cushion, protecting the brain and spine from injury. The fluid is normally clear. The test is also used to measure pressure in the spinal fluid. It is alternatively called spinal tap, ventricular puncture, lumbar puncture, cisternal puncture, cerebral spinal fluid culture.

How the test is performed?
There are different ways to get a sample of CSF. Lumbar puncture, commonly called a spinal tap, is the most common method. The test is usually done like this:

• The patient lies on his or her side, with knees pulled up toward the chest, and chin tucked downward. Sometimes the test is done with the person sitting up, but bent forward.
• After the back is cleaned, the health care provider will inject a local numbing medicine (anaesthetic) into the lower spine.
• A spinal needle is inserted, usually into the lower back area.
• Once the needle is properly positioned, CSF pressure is measured and a sample is collected.
• The needle is removed, the area is cleaned, and a bandage is placed over the needle site. The person is often asked to lie down for a short time after the test.

Occasionally, special x-rays are used to help guide the needle into the proper position. This is called fluoroscopy.

Lumbar puncture with fluid collection may also be part of other procedures, particularly a myelogram (X-ray or CT scan after dye has been inserted into the CSF).

Alternative methods of CSF collection are rarely used, but may be necessary if the person has a back deformity or an infection.

Cisternal puncture uses a needle placed below the occipital bone (back of the skull). It can be dangerous because it is so close to the brain stem. It is always done with fluoroscopy.

Ventricular puncture is even rarer, but may be recommended in people with possible brain herniation. This test is usually done in the operating room. A hole is drilled in the skull, and a needle is inserted directly into one of brain's ventricles.

CSF may also be collected from a tube that's already placed in the fluid, such as a shunt or a ventricular drain. These sorts of tubes are usually placed in the intensive care unit.

How to prepare for the test?

The patient (or guardian) must give the doctors permission to do the test.

Afterward, you should plan to rest for several hours, even if you feel fine. You won't be required to lie flat on your back the entire time, but rest is advised to prevent additional leakage of CSF around the site of the puncture.

How the test will feels?

The test is usually done with you curled up on your side with knees pulled up and chin to chest. Sometimes, CSF is collected with the person seated and bent forward over a table or chair. Holding the position may be uncomfortable, but it is extremely important to stay in this bent position to avoid moving the needle and possibly injuring the spinal cord. The person doing the test may ask you to straighten out slightly after the needle is in place, in order to accurately measure the CSF pressure, called the "opening pressure."

The anaesthetic will sting or burn when first injected. There will be a hard pressure sensation when the needle is inserted, and there is usually some brief pain when the needle goes through the tissue surrounding the spinal cord. This pain should stop in a few seconds.

Overall, discomfort is minimal to moderate. The entire procedure usually takes about 30 minutes, but it may take longer. The actual pressure measurements and CSF collection only take a few minutes.

Why the test is performed?

This test is done to measure pressures within the cerebrospinal fluid and to collect a sample of the fluid for further testing. CSF analysis can be used to diagnose certain neurological disorders, particularly infections (such as meningitis) and brain or spinal cord damage.