Table of Contents
Cerebrospinal fluid analysis is a group of laboratory tests used to diagnose a central nervous system condition such as meningitis, cancer, autoimmune disorders, bleeding around the brain, or encephalitis.
What is cerebrospinal fluid analysis?
Cerebrospinal fluid is a colourless, clear liquid. It is produced by a tissue that lines the small chambers and cavities (ventricles) in the brain called the choroid plexus. The total volume of this fluid is 3 – 5 ounces ( 90 – 150 ml) in adults, while it is 0.3 – 2 ounces (10 – 60 ml) in newborns.
It surrounds the brain and the spinal cord and acts as a cushion to protect them against injury or sudden impact. CSF also delivers nutrients and removes waste products, so it is essential for all functions of the central nervous system. CNS controls everything you do, including organ functions, muscle movement, thinking, and planning.
CSF is produced continuously and reabsorbed into your bloodstream, and it is completely replaced every few hours. Your body produces about 17 ounces (500ml) every day.
The brain is separated from the bloodstream by a protective, semi-permeable blood-brain barrier. The barrier allows crossing some substances to the brain while preventing others from passing. It keeps large molecules, most blood cells, and toxins away from the central nervous system. Any disease or condition that disturbs this sequence will change CSF’s average level or composition, so its analysis may be precious to detect many diseases affecting the central nervous system.
spinal fluid sample
Although a spinal fluid sample is more difficult to collect than a blood or urine sample, it gives accurate indications about the central nervous system’s condition. This fluid is in direct contact with the brain and the spinal cord, which is more effective in diagnosing CNS problems.
There are different methods to collect spinal fluid samples. Lumbar puncture (spinal tap) is the most common way. This cerebrospinal fluid test involves measurement of:
- CSF colour, clarity, and pressure.
- Red blood cells (RBC).
- White blood cells (WBC).
- Other foreign substances.
It can also include:
- Examination of physical characteristics and appearance.
- Detection of any microorganisms that might cause infections.
- Counts and typing of any cells present in CSF.
- Chemical tests of spinal fluid substances.
- Comparisons of similar substance levels in the blood.
A wide variety of other tests may be done, depending on the first test results and suspected condition. The required tests depend on the signs and symptoms and the alleged disease.
What is the test used for?
spinal fluid analysis is used to diagnose a wide variety of diseases and conditions that affect the brain and the spinal cord (central nervous system), including
Such as meningitis, encephalitis, fungal infections, tuberculosis, and West Nile virus. CSF analysis determines the cause of infection. It may be caused by bacteria, viruses, or less commonly by fungi, parasites, or mycobacterium tuberculosis. It may also be used to detect or near the spinal cord infections.
This test may be used to diagnose primary tumors located within the central nervous system or metastatic cancer that spreads from another part to the CNS.
- CNS autoimmune disorders
such as Guillain-Barre syndrome and multiple sclerosis. In this case, the cerebrospinal fluid analysis will look for high levels of a certain protein in the spinal fluid. These tests are known as albumin protein and IgG/albumin.
- Bleeding around the brain
Intracranial haemorrhage can be detected using spinal fluid analysis. However, the exact cause of bleeding requires additional tests. Common causes include high blood pressure and stroke.
- Alzheimer’s disease is an irreversible dementia form.
“Read also: B vitamins test”
When is the test required?
You may need a CSF analysis test if you have symptoms or signs of infections in the brain or spinal cord or autoimmune disorders such as multiple sclerosis.
Symptoms of brain and spinal cord infections
- Severe, and a sudden headache.
- Severe or prolonged nausea and vomiting.
- Stiff neck.
- Light sensitivity.
- Behaviour changes.
- Double vision.
- Confusion or hallucination.
- Loss of coordination and walking difficulty.
- Speech difficulty.
- Mood swings and depression.
- Symptoms in infants may include
- Increasing irritability and crying.
- Refuse food.
- Body stiffness.
- Bulging fontanels.
Multiple sclerosis (MS) symptoms
- Blurred vision.
- Numbness of the arms, legs, or face.
- Muscle spasms, and weakness.
- Problems of bladder control.
Symptoms of Guillain-Barre syndrome include tingling sensation and weakness of legs, arms, and the upper part of the body.
This test may be also required in some cases, such as
- You have had an injury or trauma to the brain or spinal cord.
- Cancer may spread to the brain and the spinal cord.
- Medical history and signs of any conditions affecting the central nervous system.
Normal characters of CSF
|Total volume||150 ml|
|Colour||colourless, transparent like water.|
|Opening pressure with the patient lying on lateral position||90 – 180 mm H 2O|
|Specific gravity||1.006 – 1.008|
|Osmolarity at 37°c||281 mOsm/L|
|Acid-base balance|| |
|Potassium||2.7 – 3.9 mmol/L|
|Sodium||135 – 150 mmol/L|
|Calcium||2.0 – 2.5 mEq/L (4 – 5 mg/dl)|
|Magnesium||2.0 – 2.5 mEq/L ( 2.4 – 3.1 mg/dl)|
|Chloride||116 – 127 mmol/L|
|Lactic acid||1.1 – 2.8 mmol/L|
|Lactic dehydrogenase||absolute activity depends on the testing method approximately 10% of serum value.|
|Glucose||45 – 80 mg/dl|
|Glutamine||8 – 18 mg/dl|
|Proteins||20 – 40 mg/dl according to spinal tap levels|
|Normal proteins concentration in children|| |
|Electrophoretic separation of spinal fluid proteins (% of total protein concentrations)|| |
|Erythrocyte count:|| |
Younger than 1 year
Age 1-4 years
Age 5 years to puberty
|Antibodies, viral DNA||None|
|Bacteria (Gram stain, culture, VDRL)||Negative|
What happens during the CSF analysis?
The spinal fluid sample will be taken through a procedure called a lumbar puncture that is usually done in a hospital. It is difficult to obtain spinal fluid samples. Entering a needle into the spinal canal needs complete knowledge of its anatomy and understanding any brain or spinal cord condition that might increase the procedure’s risks.
What is a lumbar puncture?
This process usually takes less than 30 minutes. It is performed by a specially trained doctor in the hospital.
The sample is usually taken from the lower part of your back or the lumbar spine. It is very important to avoid any movements during the lumbar puncture. This will help you to avoid incorrect replacement of the needle and spine trauma.
Spinal tap procedure
- You will lie on your side or remain in a sitting position on the exam table.
- Once you take the proper position, your back will be cleaned with an antiseptic.
- A local anesthetic is injected under the skin.
- A special needle will be inserted through the skin when you feel numbness in this area.
- The needle is inserted between two vertebrae into your spinal canal.
- An opening or initial pressure reading will be recorded.
- Your health care practitioner will withdraw a small amount of spinal fluid in multiple sterile vials for testing.
- This usually takes 5 minutes.
- You had to stay still during sample withdrawal.
- A closing pressure reading will be taken now.
- The needle is withdrawn then a sterile dressing and pressure will be applied to the puncture site.
- Then, you will be advised to lie in a flat position, without raising your head for one hour at least.
- This position will help you to avoid the post-test headache.
For most patients, lumbar puncture is considered a moderately uncomfortable procedure. The most common complaint is pressure sensation during entry of the needle. Tell your healthcare provider if you feel a headache or any abnormal sensation such as numbness or pain in your legs or pain at the puncture site.
How to deal with post-lumbar puncture pain?
Headache is the most common problem that may result from the spinal tap procedure. It may appear immediately after the process or up to a day or two. Lying flat without even elevating your head may help you to avoid this headache. Other ways of treatment may include drinking a sufficient amount of water (to avoid dehydration), caffeine, and pain treatment medication. Follow your doctor’s recommendations and tell him if the pain persists.
Reasons for lumbar puncture
Sometimes, spinal tap procedures may be done to introduce anaesthetics or other medication into the central nervous system instead of spinal fluid analysis. One or more spinal taps and removal of CSF may be used to decrease its pressure.
Advantages of spinal fluid over blood or urine sample
This fluid surrounds the brain and the spinal cord, so it is the best way to diagnose conditions affecting the central nervous system. CNS infections and diseases are most rapidly and easily detected with this test because these problems will affect the spinal fluid composition. Blood and urine tests may be used in conjunction with CSF analysis to evaluate your condition. However, the test’s results can not be used alone to diagnose CNS diseases.
Cerebrospinal fluid analysis results
The tests results may indicate that you have an infection, an autoimmune disorder such as multiple sclerosis, or other CNS disease. Your healthcare provider usually orders some other tests to confirm the diagnosis.
Other tests that may be required
Some tests may be required along with or after the analysis, including:
Blood culture helps to detect the presence of bacteria or fungi in the blood.
Specimens culture from other sites
Culture and/or molecular specimens testing of other possible sites of infection that led to meningitis and encephalitis.
Blood glucose and total protein
To compare with the spinal fluid glucose and protein levels.
CBC (complete blood count)
To evaluate blood cells count and abnormalities.
Blood tests (serologic tests)
To detect proteins released from disease-causing microbes (pathogens) or the antibodies that the body produces against a variety of pathogens, including waist Nile virus and other arboviruses.
CRP (C-reactive protein)
It is the most common test to detect inflammation. If it is not available, ESR (erythrocyte sedimentation rate) may be ordered instead.
CMP (comprehensive metabolic panel)
A group of tests is used to evaluate electrolyte balance and your organs’ health.
Other ways to obtain a cerebrospinal fluid sample
Sometimes, lumbar puncture can not be used because of back deformity, possible brain herniation, or infection. In these cases, more invasive methods may be used to get the spinal fluid sample.
Your healthcare specialist will drill a hole into your skull, then withdraw the sample through a needle that is inserted directly into one of your brain ventricles.
This method means inserting a needle into the back of your skull.
The sample is collected from a tube that is placed in the brain. It is usually used to release high fluid pressure.
Collecting a cerebrospinal fluid sample is usually combined with other procedures, such as inserting a dye into the fluid for a myelogram, for an X-ray and CT scan of the brain or the spinal cord.
Lumbar puncture risks
Spinal tap procedure may be associated with some primary risks such as
- Bleeding from the puncture site into the spinal fluid is called a traumatic tap.
- Discomfort sensation during and after the procedure.
- Allergic reactions to the anaesthesia.
- Headache after surgery.
- Infections at the puncture site.
There will be additional severe risks if you have a brain mass, tumour, or abscess. This mass puts pressure on the brain stem, so the spinal tap procedure may cause brain herniation, resulting in brain damage and even death. This test will not be done if a brain mass is suspected.
Patients who take blood thinners have a high risk of bleeding. Lumbar puncture is extremely dangerous for those who have clotting problems such as thrombocytopenia (low platelet count).
The ventricular and cisternal puncture may cause additional risks, such as:
- Brain or spinal cord damage.
- Bleeding within the brain.
- Blood-brain barrier disturbance.
Cerebrospinal physical features
These include pressure and appearance tests.
Fluid pressure can be measured directly in Cerebrospinal fluid analysis after opening and before closing.
Increased Cerebrospinal fluid pressure
It may occur in a variety of conditions affecting the brain and spinal cord and/or obstruct the flow of the fluid, such as
- Accumulation of the fluid in the brain.
It may be due to:
The appearance of the sample
The fluid is usually clear and colourless. Any changes in the colour will not be diagnostic, but this may indicate the presence of an additional substance. Yellow, orange, or pink fluid may refer to the breakdown of blood cells due to bleeding into the spinal fluid or the presence of bilirubin. Sometimes, Green may be seen with bilirubin or infections.
Cloudy or turbid fluid may refer to the presence of white or red blood cells, microbes, or an increase in protein levels.
Normal fluid has the same viscosity as water. If the spinal fluid is thicker, this may refer to meningitis and certain types of cancers.
Many chemical tests are used to measure the levels of chemical substances found in the spinal fluid. Most of these substances are also in the blood. The relative amount in the spinal fluid and the blood are often compared.
In typical cases, it is about ⅔ of the concentration of glucose in the blood. Glucose levels may decrease when abnormal cells are found in the fluid that metabolizes glucose. These may include white blood cells, fungi, bacteria, or cells shed by tumors.
Proteins are large molecules, so they can not cross the blood-brain barrier. Normally, only a small amount of proteins are present in the fluid. Increased proteins levels are not generally significant while decreasing their levels are most common in some cases, such as
- Brain abscess and meningitis.
- Brain or spinal cord tumors.
- Guillain-Barre syndrome.
- Multiple sclerosis.
If any of the initial tests of cerebrospinal fluid analysis are abnormal or your healthcare provider suspects a condition affecting the central nervous system. Additional tests may be required; these tests may include one or more of the following.
CSF protein electrophoresis
Separate different types of proteins. Oligoclonal bands are usually present with multiple sclerosis and sometimes some infections.
CSF immunoglobulin G
The fluid IgG increased in certain conditions such as herpes encephalitis, multiple sclerosis, and connective tissue diseases.
They are used mainly to distinguish between viral and bacterial meningitis. Lactate levels remain normal or slightly elevated in viral meningitis, while increasing in bacterial and fungal meningitis.
CSF lactate dehydrogenase (LD, LDH)
Used also in differentiating between viral and bacterial meningitis. It is increased with bacterial meningitis and remains normal in viral meningitis. It may also be elevated in leukaemia and stroke.
Myelin basic protein
Appear when nerve covering breaks down, such as in multiple sclerosis.
Increased levels of human chorionic gonadotropin (HCG), alpha-fetoprotein (AFP), and carcinoembryonic antigen (CEA) may refer to cancers that have spread from other body parts.
Amyloid-beta 42 and tau protein
For evaluation of Alzheimer’s disease in patients with its symptoms. A low Aß42 level and high tau protein level indicate an increased risk of Alzheimer’s.
This protein presents only in cerebrospinal fluid. This test is used if it is suspected that a leak of cerebrospinal fluid from the CNS is caused by trauma. A sample of the fluid leaking from the ears or the nose will be tested. A positive beta-2 protein test indicates that it is the cerebrospinal fluid.
Cell count, differential and microscopic examination
No or very few cells are present in the spinal fluid, so it appears typically clear. A microscope is used to examine a small drop of the fluid. Cells are counted manually or, in some cases, using an instrument. If the white blood cells number is very few (for example, 5 or less in the adults), a cell differential test may or may not be done.
If WBCs are numerous, differential tests should be done to identify the different types of these cells.
Cerebrospinal fluid total cell count
Red blood cells count
No RBCs are present in the spinal fluid normally, so their presence may indicate bleeding to the fluid or traumatic tap (leaking of some blood into the spinal fluid sample during spinal tap procedure).
White blood cells count
Very few WBCs are present normally. CNS infections or inflammation may increase their number significantly.
CSF White blood cells differential
Counts and identifies WBCs in different types. Small numbers of monocytes and lymphocytes are normally found in the sample.
- Neutrophiles increase with a bacterial infection.
- Lymphocytes increase with viral or fungal infections.
- Eosinophils sometimes increase with parasite infections.
- A CNS immune disorders cause a slight increase in lymphocytes.
- Leukemia spreads into the CNS cause presence of abnormal WBCs.
If abnormal cells from cancerous tumours are present in differential tests, fluid cytology should be performed.
The cerebrospinal fluid analysis sample is specially treated to look after abnormal cells by a microscope. This is used in some cases such as CNS tumors, or metastatic cancer. The presence of certain abnormal cells such as immature blood cells or tumor cells may indicate the type of cancer.
Normally, the spinal fluid does not have any bacteria, viruses, parasites, or fungi. If meningitis or encephalitis is suspected, certain tests will be performed to detect microbes. The test selection depends on signs and symptoms. These tests include
CSF Gram stain
This test can detect bacteria or fungal infections. The sample is centrifuged and the concentration is placed on a slide then treated with a specific stain. After that, it will be examined using a microscope to identify bacteria and fungi.
It is used to detect any bacteria or fungi, but a negative result does not mean that there are no infections because the microbes may be present in small concentrations or unable to grow due to prior antibiotics therapy.
This test is Used to detect nucleic acid of various pathogens by a polymerase chain reaction assay. It is helpful to detect bacterial, viral, fungal, and parasite genetic material. It may be required also in case of a negative culture test or during antibiotics therapy.
Tests for antibodies detection
The Immune system produces antibodies against specific microbes. This test may be used if molecular testing and culture are insensitive, like Lyme disease and West Nile virus.
Proteins or antigens detection
Determine proteins or antigens that are released by the microbe.
How to prepare for CSF analysis?
The cerebrospinal fluid analysis does not need any special preparation, but only you may be advised to empty your bladder and bowel before the test.
Follow up after cerebrospinal fluid analysis.
You are follow-up after CSF analysis depending on your health status and the results of the tests. You may need to undergo additional tests for a definite diagnosis.
Treatment will vary according to the conditions affecting the central nervous system. Bacterial and parasitic meningitis is a medical emergency. Their symptoms resemble viral meningitis, but they are most life-threatening. So the patient may need to use wide spectrum antibiotics until the definite cause of the meningitis is known. Early treatment may save lives and prevent CNS damage.
Cerebrospinal fluid analysis can diagnose diseases or conditions affecting the central nervous systems, such as multiple sclerosis, meningitis, and other serious infections. If your doctor ordered Cerebrospinal fluid analysis, you have to follow all the instructions to remain safe and avoid any risks.