Doctors analyze cerebrospinal fluid (CSF) to help identify conditions that affect your brain and spine. CSF samples are typically collected through a lumbar (spinal) tap.
CSF is the clear fluid that cushions and delivers nutrients to your central nervous system. Your central nervous system consists of your brain and spinal cord.
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In addition to delivering nutrients, CSF flows around your brain and spinal column, providing protection and carrying away waste.
This article takes a closer look at CSF analysis, including how CSF samples are collected, why the test might be ordered, and what may be learned through analysis.
CSF is in direct contact with your brain and spine. So, CSF analysis is more effective than a blood test for understanding central nervous system 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.
Doctors typically collect CSF samples by performing a lumbar puncture, also known as a spinal tap.
What a lumbar puncture (spinal tap) procedure involves
A lumbar puncture generally takes less than 30 minutes. A doctor who is specially trained to collect CSF performs it.
CSF is usually taken from your lower back area, called the lumbar spine. The doctor may ask you to sit and lean over so that your spine is curled forward. Or the doctor may have you lie on your side with your spine curved and your knees drawn up to your chest. Curving your spine makes a space between your bones in the lower back.
Once you’re in position, the doctor cleans your back with a sterile solution. Iodine is often used for cleaning. A sterile area is maintained throughout the procedure, which reduces the risk of infection.
The doctor then applies a numbing cream or spray to your skin. They then inject an anesthetic. Once the site is fully numb, the doctor inserts a thin spinal needle between two vertebrae. Computed tomography
The doctor will first measure the pressure inside your skull using a manometer. Both high and low CSF pressure can be signs of certain conditions.
They then collect fluid samples through the needle. When fluid collection is complete, the doctor removes the needle, cleans the puncture site again, and applies a bandage.
You’ll be asked to remain lying down for about 1 hour. This reduces the risk of headache, which is a common side effect of the procedure.
Other procedures that may be used to collect CSF
Sometimes, a person can’t have a lumbar puncture because of a back condition, 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:
- Ventricular puncture: During a ventricular puncture, a doctor drills a hole into your skull and inserts a needle directly into one of the ventricles of your brain.
- Cisternal puncture: During a cisternal puncture, a doctor inserts a needle into the back of your skull.
- Ventricular shunt: A ventricular shunt, or drain, collects CSF from a tube that a doctor places in your brain. This is done to release high fluid pressure.
A lumbar puncture (spinal tap) 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. A 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 trauma to your central nervous system. It may also be used if you have cancer and your doctor wants to see whether the cancer has spread to the central nervous system.
In addition, CSF analysis may be ordered if you have one or more of the following symptoms:
- severe, constant headache
- stiff neck
- hallucinations, confusion, or dementia
- seizures
- 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
- dizziness
- speaking difficulties
- trouble walking or poor coordination
- severe mood changes
- treatment-resistant depression
Doctors use CSF samples to examine and measure the following:
- fluid pressure
- proteins
- glucose, or blood sugar
- glutamine
- red blood cells
- white blood cells
- lactate dehydrogenase, which is a blood enzyme
- chemicals
- bacteria
- chloride
- antigens, or harmful substances produced by invading microorganisms
- total proteins
- oligoclonal bands, which are specific proteins
- cancer cells
- viruses
- viral DNA
- other invasive organisms or foreign substances
- antibodies against viruses
Medical analysis can also 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 analysis can accurately distinguish between a wide range of central nervous system diseases that can otherwise be difficult to diagnose. Conditions found by CSF analysis include:
Infectious diseases
Viruses, bacteria, fungi, and parasites can all infect the central nervous system. CSF analysis can find certain infections. For example, common central nervous system infections include:
- meningitis
- encephalitis
- tuberculosis
- fungal infections
- West Nile virus
- Eastern equine encephalitis virus (EEEV)
Hemorrhaging
CSF analysis can detect intracranial bleeding. 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 central nervous system through inflammation, destruction of the myelin sheath around the nerves, and antibody production.
Common diseases of this type include:
Tumors
CSF analysis can detect primary tumors in the brain or spine. It can also detect metastatic cancers that have spread to your central nervous system from other body parts.
Doctors sometimes use CSF analysis to help diagnose multiple sclerosis (MS). Doctors can use the test to rule out other medical conditions with similar symptoms and look for signs of MS, such as:
- elevated levels of antibodies called IgG antibodies
- proteins called oligoclonal bands
- an unusually high number of white blood cells
Examining the proteins in CSF may also help doctors 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.
Normal results mean that nothing abnormal was found in the spinal fluid. All measured levels of CSF components were found to be within a normal range.
The following conditions may cause abnormal results:
- a tumor
- metastatic cancer
- hemorrhaging
- encephalitis, which is an inflammation of the brain
- an infection
- inflammation
- Reye syndrome, which is a rare, life threatening 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 exposure to a virus
- sarcoidosis, which is a granulomatous (tissue growth-causing) condition of unknown cause affecting many organs, primarily the lungs, joints, and skin
- neurosyphilis, which happens when an infection with syphilis involves your brain
- MS, which is an autoimmune disorder that affects your brain and spinal cord
Your follow-up and outlook will depend on what caused your abnormal CSF test results. Further testing will most likely be required to get a definitive diagnosis.
A cerebrospinal fluid (CSF) analysis identifies and measures the chemicals and other substances in the fluid that surrounds your brain and spinal cord.
This analysis can help doctors diagnose a number of conditions, from infections and autoimmune disorders to brain tumors and intracranial bleeding.
CSF samples are typically collected through a lumbar puncture (spinal tap).
A doctor may order a CSF analysis if you’ve had trauma to your central nervous system. It may also be used if you have cancer and your doctor wants to see whether the cancer has spread to the central nervous system or to help diagnose multiple sclerosis.