Cerebrospinal fluid (CSF) is a clear liquid that cushions and surrounds the brain and spinal cord. It delivers nutrients and carries away waste. 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 patient’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/or spinal cord, and cancer.
Although obtaining a spinal fluid sample is difficult, testing a CSF sample is one of the best ways to correctly diagnose specific conditions because CSF is in direct contact with the brain and spine.
The most common method of collecting cerebrospinal fluid is a lumbar puncture, sometimes called a spinal tap.
Cerebrospinal fluid analysis; spinal fluid analysis; cell count and differential – CSF; CSF Cell Count and Cell Differential
CSF cell count and differential cell count are often ordered for patients who have cancer or have suffered trauma to the brain or spinal cord. The test may also be done when infectious diseases (such as bacterial meningitis), hemorrhaging (bleeding), or immune response disorders such as multiple sclerosis are suspected as possible causes of a patient’s symptoms.
Symptoms that may prompt CSF analysis include:
- severe headache
- stiff neck
- hallucinations, confusion, or dementia
- 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
- speaking difficulties
- trouble walking or poor coordination
- mood swings or depression
A lumbar puncture usually takes less than 30 minutes and is performed by a physician specially trained to safely collect CSF.
CSF is usually withdrawn from the lower back area. It is 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 is applied to the skin, and then 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 (opening pressure) is usually measured using a manometer (pressure gauge). High or low CSF pressure can be signs of certain conditions and diseases, including meningitis, intracranial hemorrhage (bleeding in the brain), and tumors. Pressure may also be measured at the end of the procedure (closing pressure).
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 removed the needle from your back. The puncture site is cleaned again with sterile solution, and a bandage is applied.
You must remain lying down for about one hour to avoid headache, a common side effect of the procedure.
Rarely, if you have a back deformity, infection, or possible brain herniation (when structures of the brain have shifted out of place), 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.
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 (Coumadin) because you may need to stop taking them for a couple of days before the procedure.
Before the procedure, you will 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)
If you take blood thinners, your risk of bleeding is higher.
There are serious additional risks for patients who have a brain mass such as a tumor or abscess (puss surrounded by inflamed tissue) putting pressure on the brain stem. In these cases, lumbar puncture can cause brain herniation. Brain herniation results in high intracranial pressure, which can eventually cut off the supply of blood to the brain. This can result in brain damage or even death. If a brain mass is suspected, lumber puncture will not be performed.
Cisternal and ventricular puncture have additional risks. These procedures may cause damage to spinal cord or brain, bleeding within the brain, or disturbance of the blood/brain barrier in the skull.
Lumbar puncture is extremely dangerous for people who have low platelet count (thrombocytopenia) 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 (agents that cause disease, such as viruses).
- Eosinophils normally make up only about three percent of the total WBC count. These cells are thought to resist certain infections and parasites and respond to allergens.
CSF Cell Count
Normally, there are no RBCs in the cerebrospinal fluid, and there should be no more than five WBCs per cubic millimeter (mm3) 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 (AACC, 2012).
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. This infection is hard to diagnose because its symptoms are similar to viral meningitis, a less life-threatening illness. Prompt treatment is essential. The doctor may put you on broad-spectrum antibiotics (medication that treats a variety of bacteria types) while conducting additional tests to find the exact cause of the infection.