There are different ways to get a sample of CSF. Lumbar puncture (spinal tap) is the most common method.
To have the test:
You will lie on your side with your knees pulled up toward the chest, and chin tucked downward. Sometimes the test is done sitting up, but bent forward.
After the back is cleaned, the health care provider will inject a local numbing medicine (anesthetic) into the lower spine.
A spinal needle will be inserted.
Once the needle is in position, the CSF pressure is measured and a sample of 1 to 10 mL of CSF is collected.
The needle is removed, the area is cleaned, and a bandage is placed over the needle site. You may be asked to remain lying down for a short time after the test.
Occasionally, special x-rays are used to help guide the needle into position. This is called fluoroscopy.
Lumbar puncture with fluid collection may also be part of other procedures such as an x-ray or CT scan after dye has been inserted into the CSF.
Rarely, other methods of CSF collection may be used.
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 may be recommended in people with possible brain herniation. This is a very rarely used method. It is most often done in the operating room. A hole is drilled in the skull, and a needle is inserted directly into one of the 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.
How to Prepare for the Test
You will need to give the health care team your consent before the test.
Afterward, you should plan to rest for several hours, even if you feel fine. This is to prevent fluid from leaking around the site of the puncture. You will not need to lie flat on your back the entire time.
How the Test will Feel
It may be uncomfortable to stay in position for the test. Staying still is important because movement may lead to injury of the spinal cord.
You may be told to straighten your position slightly after the needle is in place. This is to help measure the CSF pressure.
The anesthetic will sting or burn when first injected. There will be a hard pressure sensation when the needle is inserted. Often, there is some brief pain when the needle goes through the tissue surrounding the spinal cord. This pain should stop in a few seconds.
In most cases, the procedure takes about 30 minutes. 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 neurologic disorders. These may include infections (such as meningitis) and brain or spinal cord damage. A spinal tap may also be done to establish the diagnosis of normal pressure hydrocephalus.
CSF glucose: 50 to 80 mg/100 mL (or greater than two-thirds of blood sugar level)
CSF cell count: 0 to 5 white blood cells (all mononuclear), and no red blood cells
Chloride: 110 to 125 mEq/L
Normal value ranges may vary slightly among different laboratories. Talk to your provider about the meaning of your specific test results.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
What Abnormal Results Mean
If the CSF looks cloudy, it could mean there is an infection or a buildup of white blood cells or protein.
If the CSF looks bloody or red, it may be a sign of bleeding or spinal cord obstruction. If it is brown, orange, or yellow, it may be a sign of increased CSF protein or previous bleeding (more than 3 days ago). There may be blood in the sample that came from the spinal tap itself. This makes it harder to interpret the test results.
Bleeding into the spinal canal or around the brain (subdural hematomas).
Discomfort during the test
Headache after the test that can last a few hours or days. If headaches last more than a few days (especially when you sit, stand or walk) you might have a CSF-leak. You should talk to your physician if this occurs.
Hypersensitivity (allergic) reaction to the anesthetic
Infection introduced by the needle going through the skin
There is an increased risk of bleeding in people who take blood thinners.
Brain herniation may occur if this test is done on a person with a mass in the brain (such as a tumor or abscess). This can result in brain damage or death. This test is not done if an exam or test reveals signs of a brain mass.
Damage to the nerves in the spinal cord may occur, particularly if the person moves during the test.
Cisternal puncture or ventricular puncture carries additional risks of brain or spinal cord damage and bleeding within the brain.
This test is more dangerous for people with:
A tumor in the back of the brain that is pressing down on the brainstem
Blood clotting problems
Low platelet count (thrombocytopenia)
Individuals taking blood thinners, aspirin, clopidogrel, or other similar drugs to decrease the formation of blood clots.
Griggs RC, Jozefowicz RF, Aminoff MJ. Approach to the patient with neurologic disease. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 396.
Daniel Kantor, MD, Kantor Neurology, Coconut Creek, FL and Immediate Past President of the Florida Society of Neurology (FSN). Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.