Cerebrospinal Fluid Analysis
Reviewed by: HU Medical Review Board | Last updated: June 2022
Cerebrospinal fluid (CSF) is a clear, colorless fluid produced in the brain. This fluid surrounds the brain and spinal cord to provide cushion and protection. CSF also delivers nutrients to the brain and spinal cord, and it helps the brain get rid of waste products.1,2
If your doctor thinks you may have multiple sclerosis (MS), they may order CSF analysis as part of a larger panel of tests.3
What is CSF analysis?
CSF analysis is a test used to see what is in a person's CSF. This can help doctors determine the cause of specific symptoms or problems. The test can also help doctors monitor the progress of some brain and nerve (neurological) diseases. CSF analysis is performed after a procedure called a spinal tap (or lumbar puncture).1,3,4
How is a spinal tap performed?
A spinal tap is a procedure used to collect a sample of CSF. This sample is then analyzed in a lab.4
The test involves inserting a needle into the spinal canal. You will either lie on your side with your knees drawn up to your chest or sit up and lean over with your back arched. These positions help open up the spinal canal and make it easier for the doctor to insert the needle.4
The doctor will insert the needle between the vertebrae in the lower back. Nerves that branch off of the spinal cord are located in this area.4
A spinal tap is performed using local anesthesia. This numbs the area and helps to decrease discomfort. Local anesthesia causes brief stinging and burning when injected but then numbs the area. It takes about 30 minutes to complete the procedure.4
How does CSF analysis help diagnose MS?
There is no single test that can diagnose MS. However, CSF analysis may be used as part of a panel of tests to help doctors diagnose MS and rule out other medical conditions. CSF analysis can help identify specific proteins that are associated with the disease.3
CSF typically contains sugar (glucose), proteins, and other substances found in the blood. Oligoclonal bands (O-bands) are a specific type of protein found in the CSF of most people with MS. The presence of these proteins can help doctors diagnose MS.2,3
O-bands are not always present in people with MS. They may also be found with other conditions, such as Alzheimer's disease, Parkinson's disease, and other brain disorders. For this reason, CSF analysis is not the only test to diagnose MS.3,4
What are the possible side effects of CSF analysis?
A spinal tap is a common bedside procedure performed by neurologists. As with other procedures, spinal taps have potential risks. The risks and possible side effects include the following.
While some people experience little to no pain with a spinal tap, the procedure can cause pain, tenderness, or discomfort in your lower back. During the test, you may feel a lot of pressure. After the procedure, your back might be sore. You also might feel pain moving down your leg. This usually lasts only a few hours.5
About 1 in 4 people report a headache after a spinal tap. Headaches result from the temporary decrease in the amount of CSF surrounding the brain and spinal cord. This decrease lessens the pressure around the brain. This kind of headache (a “low-pressure” headache) is worse when sitting or standing and better when lying down.5
The headache typically starts minutes to hours after the procedure and typically resolves within 24 hours. Staying hydrated and drinking caffeine can help.5
In rarer cases, the headache can persist for several days due to continued slow leakage of CSF. In most of these cases, the leak and headache resolve within a week. However, sometimes people need to have another procedure to repair the CSF leak causing the headache.5
The site on your back where the doctor inserted the needle might bleed. Bleeding also can happen in your spine, but this is rare. Your doctor can do a blood test before your spinal tap to make sure you are not at higher risk for bleeding.5
Brain stem herniation
This is a rare complication that usually results from a brain tumor or large lesion in the brain. When CSF is removed, the change in pressure inside the brain forces the brainstem through the hole in the base of the skull. This medical emergency most often results in rapid paralysis and death. Your doctor can do brain imaging before your spinal tap to look for any tumor or lesion that may put you at risk for this rare complication.5
These are not all the possible side effects of CSF analysis and spinal tap. Talk to your doctor about what to expect with a spinal tap. You also should call your doctor if you have any changes that concern you after the spinal tap.5
Things to know about CSF analysis
Before you have a CSF analysis, tell your doctor about any allergies or medical conditions. Also, let your doctor know if you take any medicines. Include over-the-counter drugs and supplements.5
Your doctor will let you know how to prepare for the procedure. They will give you instructions about what you can eat and drink before and after the test.5
The test is usually done at your doctor’s office or an outpatient facility. Your doctor will give you aftercare instructions. Plan to rest for several hours to a day after the procedure.5