CEREBRAL SPINAL FLUID (CSF) ANALYSIS
WHAT IS A CSF ANALYSIS?
Cerebrospinal fluid (CSF) analysis is a way of looking for conditions that affect the brain and spine. It is a series of laboratory tests performed on a sample of CSF. CSF is the clear fluid that cushions and delivers nutrients to the central nervous system (CNS). The CNS consists of the brain and spinal cord.
CSF is produced by the choroid plexus in the brain, and then reabsorbed into the bloodstream. The fluid is completely replaced every few hours. In addition to delivering nutrients, CSF flows around the brain and spinal column, providing protection and carrying away waste.
CEREBRAL SPINAL FLUID (CSF) COLLECTION
Cerebrospinal fluid (CSF) collection is a test to look at the fluid that surrounds the brain and spinal cord.
CSF acts as a cushion, protecting the brain and spine from injury. The fluid is normally clear. It has the same consistency as water. The test is also used to measure pressure in the spinal fluid.
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 do not need lie flat on your back the entire time.
HOW THE TEST IS PERFORMED?
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 oftendone 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.
CSF ANALYSIS USE
A CSF sample is commonly collected by performing a lumbar puncture (also known as a “spinal tap”). An analysis of the sample involves the measurement and examination for:
- fluid pressure
- red blood cells
- white blood cells
- other invasive organisms or foreign substances
- measurement of the physical characteristics and appearance of CSF
- chemical tests on substances found in spinal fluid (comparisons to levels of the similar substances found in the blood maybe made).
- cell counts and typing of any cells found in the CSF
- identification of any microorganisms that could cause infectious diseases
CSF is in direct contact with the brain and spine. Therefore, CSF analysis is more effective than a blood test for understanding CNS symptoms. However, it is more difficult to obtain a spinal fluid sample than a blood sample. Entering the spinal canal with a needle requires expert knowledge of the anatomy of the spinal structures and a clear understanding of any underlying brain or spinal conditions that might increase the risk of complications from the procedure.