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.
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 of and examination for:
- fluid pressure
- red blood cells
- white blood cells
- other invasive organisms or foreign substances
. Analysis includes:
- 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.
A lumbar puncture usually takes less than 30 minutes. It is performed by a physician specially trained to collect CSF.
CSF is usually taken from the lower back area—the lumbar spine. It is very important to remain completely still during the procedure. This way you avoid incorrect needle placement or trauma to your spine.
You may be seated with the spine curled forward. You may also lie on your side with the spine curved and your knees drawn up to the chest. Curving your spine makes a space between the bones in the lower back.
Once you are in position, your back will be cleaned with a sterile solution. Iodine is often used for cleaning. A sterile area is maintained throughout the procedure. This reduces the risk of infection.
A numbing cream is applied to the skin. Then you will be injected with anesthetic. Once the site is fully numb, your doctor will insert a thin spinal needle between two vertebrae. Sometimes a special type of X-ray called fluoroscopy is used to guide the needle.
First, CSF pressure (opening pressure) is measured using a manometer. Both high and low CSF pressure can be signs of certain conditions.
Fluid samples are then taken through the needle. When fluid collection is complete, the needle is taken out. The puncture site is cleaned again. A bandage is applied.
You will be told to remain lying down for about one hour. This reduces the risk of headache—a common side effect of the procedure.
Sometimes a patient cannot have a lumbar puncture because of a back deformity, infection, or possible brain herniation. Then more invasive CSF collection methods must be used. These methods require hospitalization. They include:
- ventricular puncture: a hole is drilled into the skull, and a needle is inserted directly into one of the ventricles of the brain
- cisternal puncture: a needle is inserted into the back of the skull
- ventricular shunt or drain: collection of CSF from a tube that has been placed in the brain to release high fluid pressure
CSF collection is often combined with other procedures. For example, dye might be inserted into the CSF for a myelogram. This is an X-ray or CT scan of the brain and spine.
This test requires a signed release. You will have to state that you understand the risks of the procedure. Before the test, you’ll 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
Patients who take blood thinners have a heightened risk of bleeding. Lumbar puncture is extremely dangerous for people who have low platelet count (thrombocytopenia) or other clotting problems.
There are serious additional risks for patients who have a brain mass, tumor, or abscess. These conditions put pressure on the brain stem. A lumbar puncture could then cause brain herniation to occur. This can result in brain damage or even death.
Brain herniation is a shifting of structures of the brain. It is usually accompanied by high intracranial pressure. The condition eventually cuts off blood supply to the brain. This causes irreparable damage. If a brain mass is suspected, the test will not be done.
Cisternal and ventricular puncture methods carry additional risks. These risks include:
- damage to spinal cord or brain
- bleeding within the brain
- disturbance of the blood/brain barrier
In addition, CSF analysis may be ordered when a patient has one or more of the following symptoms:
- severe, unremitting headache
- stiff neck
- hallucinations, confusion, or dementia
- flu-like symptoms that persist or intensify
- fatigue, lethargy, muscle weakness
- changes in consciousness
- severe nausea
- fever or rash
- light sensitivity
- numbness or tremor
- speaking difficulties
- trouble walking or poor coordination
- severe mood swings
- intractable clinical depression
CSF analysis can accurately distinguish between a wide range of CNS diseases, which can otherwise be difficult to diagnose. Conditions found by CSF analysis can be placed into four main categories: infectious diseases, hemorrhaging, immune response disorders, and tumors.
Viruses, bacteria, fungi, and parasites can all infect the CNS. Common CNS infections include:
- fungal infections
- West Nile virus
- eastern equine virus
Intracranial bleeding can be detected by CSF analysis. However, isolating the exact cause of bleeding may require additional scans or tests. Common causes include:
- high blood pressure
Immune Response Disorders
The immune system can cause damage to the CNS through:
- destruction of the myelin sheath around the nerves
- antibody production
Common diseases of this type include:
- Guillain-Barré syndrome
- multiple sclerosis
CSF analysis can detect primary tumors in the brain or spine. It can also detect metastatic cancers that have spread to the CNS from other body parts.
The following are often measured in CSF analysis:
- white blood cell count
- red blood cell count
- glucose (blood sugar)
- lactate dehydrogenase (blood enzyme)
- antigens (harmful substances produced by invading microorganisms)
- total proteins
- oligoclonal bands (specific proteins)
- cancer cells
- viral DNA
- antibodies against viruses
Normal results mean that nothing abnormal was found in the spinal fluid. All measured levels of CSF components were found to be within normal range.
Abnormal results may be caused by one of the following:
- a tumor
- metastatic cancer
- encephalitis (inflammation of the brain)
- Reye syndrome (a rare, often fatal disease affecting children and associated with viral infections and aspirin ingestion))
- meningitis (from fungus, tuberculosis, virus, or bacteria)
- viruses such as West Nile or eastern equine
- Guillain-Barré syndrome (an autoimmune condition that causes paralysis and occurs post-viral exposure)
- sarcoidosis (granulomatous condition of unknown cause affecting many organs, primarily the lungs, joints and skin)
- neurosyphilis (brain involvement from infection with syphilis)
- multiple sclerosis (an autoimmune disorder that affects the brain and spinal cord)
If an abnormal CNS test is reported, follow-up and outlook depend on the cause of the problem. Further testing will most likely be required in order to get a definitive diagnosis. Treatment and outcomes will vary.
Meningitis caused by a bacterial or parasitic infection is a medical emergency. Symptoms are similar to viral meningitis. However, viral meningitis is less life-threatening.
If you have bacterial meningitis you may receive broad-spectrum antibiotics until the cause of the infection is determined. Prompt treatment is essential to save your life. It can also prevent permanent CNS damage.