Cerebrospinal fluid (CSF) is a clear liquid that cushions and surrounds the brain and spinal cord. It helps support the venous structures around the brain, and it’s important in brain homeostasis and metabolism. This fluid is continually replenished by the choroid plexus in the brain and absorbed into the bloodstream. The body completely replaces CSF every few hours.
CSF cell count and differential cell count are two components in a series of laboratory tests performed to analyze a person’s CSF. These tests are helpful in diagnosing diseases and conditions of the central nervous system, which includes your brain and spinal cord. Conditions of the central nervous system include meningitis, which causes inflammation of the brain and spinal cord, multiple sclerosis, hemorrhage around the brain, and cancer with brain involvement.
Although obtaining a spinal fluid sample is a bit painful, testing a CSF sample is one of the best ways to correctly diagnose specific conditions. This is because CSF is in direct contact with the brain and spinal cord.
The most common method of collecting cerebrospinal fluid is a lumbar puncture, sometimes called a spinal tap.
CSF cell count and differential cell count may be ordered for people who have cancer with associated confusion or who have experienced trauma to the brain or spinal cord. The test may also be done when infectious diseases, hemorrhaging, or immune response disorders are suspected as possible causes of a person’s symptoms.
Symptoms that may prompt CSF analysis include:
- severe headache
- stiff neck
- hallucinations or confusion
- flu-like symptoms that persist or intensify
- fatigue, lethargy, or muscle weakness
- changes in consciousness
- severe nausea
- fever or rash
- light sensitivity
- numbness or tremor
- trouble walking or poor coordination
A lumbar puncture usually takes less than 30 minutes and is performed by a doctor specially trained to safely collect CSF.
CSF is usually withdrawn from the lower back area. It’s very important to remain completely still to avoid incorrect needle placement or trauma to the spine. If you think you will have trouble staying still, tell your doctor in advance.
You will either be seated with your spine curled forward or lie on your side with your spine curved and your knees drawn up to your chest. Curving the spine allows the doctor to find ample space to insert a thin spinal needle between the bones in the lower back (vertebrae). Sometimes fluoroscopy (X-ray) is used to guide the needle safely between the vertebrae.
When you are in position, the doctor or a nurse will clean your back with a sterile solution such as iodine. A sterile area is maintained throughout the procedure to lower the risk of infection.
Numbing cream may be applied to the skin before the site is injected with an anesthetic (pain-killing) solution. When the site is numb, the doctor inserts the spinal needle.
Once the needle is in, CSF pressure is usually measured using a manometer, or pressure gauge. High CSF pressure can be a sign of certain conditions and diseases, including meningitis, bleeding in the brain, and tumors. Pressure may also be measured at the end of the procedure.
The doctor then takes fluid samples up through the needle and into an attached syringe. Several vials of fluid may be taken.
When fluid collection is complete, the doctor removes the needle from your back. The puncture site is cleaned again with sterile solution, and a bandage is applied.
If your doctor suspects that you have a brain tumor, brain abscess, or brain swelling, he or she will probably order a CT scan of your brain before attempting the spinal tap to make sure that it’s safe to perform the procedure.
In these cases, lumbar puncture can cause brain herniation, which occurs when part of the brain becomes trapped in the opening of the skull where the spinal cord exits. It can cut off the supply of blood to the brain and result in brain damage or even death. If a brain mass is suspected, lumber puncture will not be performed.
Rarely, if you have a back deformity, infection, possible brain herniation, or increased pressure around the brain due to a tumor, abscess, or swelling, it is necessary to use more invasive CSF collection methods. These methods usually require hospitalization. They include:
- Ventricular puncture: A doctor drills a hole into the skull and inserts a needle directly into one of the ventricles of the brain.
- Cisternal puncture: A doctor inserts a needle below the base of the skull.
Cisternal and ventricular puncture have additional risks. These procedures may cause damage to the spinal cord or brain, bleeding within the brain, or disturbance of the blood/brain barrier in the skull.
A lumbar puncture requires a signed release stating that you understand the risks of the procedure.
Be sure to tell your doctor if you take any blood-thinning medications, such as warfarin, because you may need to stop taking them for a couple of days before the procedure.
Before the procedure, you may be asked to empty your bowels and bladder.
Primary risks associated with lumbar puncture include:
- bleeding from the puncture site into the spinal fluid (traumatic tap)
- discomfort during and after the procedure
- allergic reaction to the anesthetic
- infection at the puncture site
- headache after the test
- damage to spinal cord nerves, especially if you move during the procedure
- persistent leaking of the CSF at the puncture site after the procedures
If you take blood thinners, your risk of bleeding is higher.
Lumbar puncture is extremely dangerous for people who have low platelet count or other blood clotting problems.
The CSF cell count and differential cell count involve microscopic examination of blood cells and their components in a laboratory.
CSF cell count
In this test, a lab technician counts the number of red blood cells (RBCs) and white blood cells (WBCs) present in a drop of your fluid sample.
CSF differential cell count
For a CSF differential cell count, a lab technician examines the types of WBCs found in the CSF sample and counts them. He or she also looks for foreign or abnormal cells. Dyes are used to help separate and identify cells.
There are several types of WBCs in the body:
- Lymphocytes normally make up 25 percent or more of the total WBC count. There are two forms: B cells, which make antibodies, and T cells, which recognize and remove foreign substances.
- Monocytes normally make up 10 percent or less of the total WBC count. They ingest bacteria and other foreign particles.
- Neutrophils are the most abundant type of WBC in healthy adults. They perform an essential role in the body’s immune system and are the first line of defense against pathogens.
- Eosinophils normally make up only about 3 percent of the total WBC count. These cells are thought to resist certain infections and parasites and respond to allergens.
Understanding your results
CSF cell count
Normally, there are no RBCs in the cerebrospinal fluid, and there should be no more than five WBCs per cubic millimeter of CSF.
If your fluid contains RBCs, this may indicate bleeding. It is also possible that you had a traumatic tap (blood leaked into the fluid sample during collection). If you had more than one vial collected during your lumbar puncture, these will be checked for RBC to test the bleeding diagnosis.
A high WBC count may indicate infection, inflammation, or bleeding. The associated conditions may include:
- intracranial hemorrhage (bleeding in the skull)
- multiple sclerosis
Differential cell count
Normal results mean that normal cell counts were found, and the counts and ratios of the various types of white blood cells were within normal range. No foreign cells were found.
Increases, however slight, in your WBC counts may indicate certain kinds of infection or disease. For example, a viral or fungal infection may cause you to have more lymphocytes.
The presence of abnormal cells may indicate cancerous tumors.
If abnormalities are found by the CSF cell count and differential cell count, further tests may be needed. Appropriate treatment will be provided based on the condition that is found to be causing your symptoms.
If test results suggest bacterial meningitis, it is a medical emergency. Prompt treatment is essential. The doctor may put you on broad-spectrum antibiotics while conducting additional tests to find the exact cause of the infection.