Cerebrospinal fluid (CSF) analysis is a way of looking for conditions that affect your brain and spine. It’s a series of laboratory tests performed on a sample of CSF. CSF is the clear fluid that cushions and delivers nutrients to your 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 your bloodstream. The fluid is completely replaced every few hours. In addition to delivering nutrients, CSF flows around your brain and spinal column, providing protection and carrying away waste.
A CSF sample is commonly collected by performing a lumbar puncture, which is 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 can include:
- measurement of the physical characteristics and appearance of CSF
- chemical tests on substances found in your spinal fluid or comparisons to levels of similar substances found in your blood
- cell counts and typing of any cells found in your CSF
- identification of any microorganisms that could cause infectious diseases
CSF is in direct contact with your brain and spine. So CSF analysis is more effective than a blood test for understanding CNS symptoms. However, it’s more difficult to obtain a spinal fluid sample than a blood sample. Entering the spinal canal with a needle requires expert knowledge of the spine’s anatomy and a clear understanding of any underlying brain or spinal conditions that might increase the risk of complications from the procedure.
A lumbar puncture generally takes less than 30 minutes. It’s performed by a doctor who is specially trained to collect CSF.
CSF is usually taken from your lower back area, or the lumbar spine. It’s 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 and asked to lean over so that your spine is curled forward. Or your doctor may have you may lie on your side with your spine curved and your knees drawn up to the chest. Curving your spine makes a space between your bones in the lower back.
Once you’re in position, your back is 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 or spray is applied to your skin. Your doctor then injects anesthetic. Once the site is fully numb, your doctor inserts a thin spinal needle between two vertebrae. A special type of X-ray called fluoroscopy is sometimes used to guide the needle.
First, the pressure inside the skull 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 removed. The puncture site is cleaned again. A bandage is applied.
You’ll be asked to remain lying down for about one hour. This reduces the risk of a headache, which is a common side effect of the procedure.
Sometimes a person can’t have a lumbar puncture because of a back deformity, infection, or possible brain herniation. In these cases, a more invasive CSF collection method that requires hospitalization might be used, such as one of the following:
- During a ventricular puncture, your doctor drills a hole into your skull and inserts a needle directly into one of the ventricles of your brain.
- During a cisternal puncture, your doctor inserts a needle into the back of your skull.
- A ventricular shunt or drain can collect CSF from a tube that your doctor places in your brain. This is done to release high fluid pressure.
This test requires a signed release that states you understand the risks of the procedure.
Primary risks associated with lumbar puncture include:
- bleeding from the puncture site into the spinal fluid, which is called a traumatic tap
- discomfort during and after the procedure
- an allergic reaction to the anesthetic
- an infection at the puncture site
- a headache after the test
People who take blood thinners have a heightened risk of bleeding. Lumbar puncture is extremely dangerous for people who have clotting problems such as a low platelet count, which is called thrombocytopenia.
There are serious additional risks if you have a brain mass, tumor, or abscess. These conditions put pressure on your 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’s usually accompanied by high intracranial pressure. The condition eventually cuts off blood supply to your brain. This causes irreparable damage. The test won’t be done if a brain mass is suspected.
Cisternal and ventricular puncture methods carry additional risks. These risks include:
- damage to your spinal cord or brain
- bleeding within your brain
- disturbance of the blood-brain barrier
CSF analysis may be ordered if you’ve had CNS trauma. It may also be used if you have cancer and your doctor wants to see if the cancer has spread to the CNS.
In addition, CSF analysis may be ordered if you have 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, or 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 that can otherwise be difficult to diagnose. Conditions found by CSF analysis include:
Viruses, bacteria, fungi, and parasites can all infect the CNS. Certain infections can be found by CSF analysis. Common CNS infections include:
- fungal infections
- West Nile virus
- eastern equine encephalitis virus (EEEV)
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, stroke, or an aneurysm.
Immune response disorders
CSF analysis can detect immune response disorders. The immune system can cause damage to the CNS through inflammation, destruction of the myelin sheath around the nerves, and antibody production.
Common diseases of this type include:
CSF analysis can detect primary tumors in the brain or spine. It can also detect metastatic cancers that have spread to your CNS from other body parts.
CSF analysis may also be used to help diagnose multiple sclerosis (MS). MS is a chronic condition in which your immune system destroys the protective covering of your nerves, which is called myelin. People with MS may have a variety of symptoms that are constant or come and go. They include numbness or pain in their arms and legs, vision problems, and trouble walking.
CSF analysis may be done to rule out other medical conditions that have symptoms similar to MS. The fluid may also show signs that your immune system isn’t functioning normally. This can include high levels of IgG (a type of antibody) and the presence of certain proteins that form when myelin breaks down. About 85 to 90 percent of people with MS have these abnormalities in their cerebral spinal fluid.
Some types of MS progress quickly and can be life-threatening within weeks or months. Looking at the proteins in CSF may enable doctors to develop “keys” called biomarkers. Biomarkers can help identify the type of MS you have earlier and more easily. Early diagnosis could allow you to get treatment that could extend your life if you have a form of MS that’s rapidly progressing.
The following are often measured in CSF analysis:
- white blood cell count
- red blood cell count
- glucose, or blood sugar
- lactate dehydrogenase, which is a blood enzyme
- antigens, or harmful substances produced by invading microorganisms
- total proteins
- oligoclonal bands, which are 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, which is an inflammation of the brain
- an infection
- Reye’s syndrome, which is a rare, often fatal disease affecting children that’s associated with viral infections and aspirin ingestion
- meningitis, which you can get from fungi, tuberculosis, viruses, or bacteria
- viruses such as West Nile or Eastern equine
- Guillain-Barré syndrome, which is an autoimmune condition that causes paralysis and occurs after viral exposure
- sarcoidosis, which is a granulomatous condition of unknown cause affecting many organs (primarily the lungs, joints, and skin)
- neurosyphilis, which happens when an infection with syphilis involves your brain
- multiple sclerosis, which is an autoimmune disorder that affects your brain and spinal cord
Your follow-up and outlook will depend on what caused your CNS test to be abnormal. 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.
People with bacterial meningitis 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.