Examination of Cerebrospinal Fluid (CSF)

The Cerebro Spinal Fluid (CSF) is formed by selective dialysis of Plasma by the choroid plexus of the ventricles of the brain. Through the foramina in the 4th ventricle it then passes into the subarachnoidal cisterns at the base of the brain and travels over the surface of the cerebral hemispheres. It is finally absorbed into the blood in the cerebral veins and rural sinuses. CSF is present in the cavity that surrounds the brain in the skull and the spinal cord in the spinal colum. The volume of CSF (adult) is about 150 ml. CSF performs flowing functions .

  1. It helps to protect the brain and spinal cord from injury by acting like a fluid buffer.
  2. It also acts as a medium for transfer of substances from the brain tissue and spinal cord to blood.

Normal Composition of CSF

  1. Color : Colorless
  2. pH : 7.3 – 7.4
  3. Appearance : Clear
  4. No clot formation on standing
  5. Specific gravity : 1.003 – 1.008
  6. Total solids : 0.85 – 1.70 g/dl
  • Protein : 15 – 45 mg/dl ( album in: 50 – 70% and globulin : 30 – 50%)
  • Glucose : 40 – 80%
  • Chloride : 700 – 750 mEq/l
  • Sodium : 144 – 154 mEq/l
  • Potassium : 2.0 – 3.5 mEq/l
  • Creatinine : 0.5 – 1.2 mg/dl
  • Cholesterol : 0.2 – 0.6 mg/dl
  • Ures : 6 – 16 g/dl
  • Uric acid : 0.5 – 4.5 mg/dl

7. Cells : 0 – 8 Lymphocyte/ per Cumm (μL) ( Neutrophils : absent)

Clinical Significance

CSF examination is carried out in the laboratory mainly for the diagnosis of meningitis. It is inflammation of the meninges, the lining of the skull and covering of the brain and spinal colum. Meningitis causes disturbance in the central nervous system. The Other clinical conditions in the which CSF examination may be required are encephalitis, subarachonoid hemorrage, spinal cord tumor, multiple sclerosis, central nervous system syphilis etc. CSF examination is also carried out in the treatments of elevated CSF pressure in selected patient with benign intracranial hypertension.

Following are the changes observed in CSF in various clinical conditions

Bacterial infection

  1. Appearance : Cloudy
  2. Cells/ Cumm (μL) : >500 Neutrophils
  3. Glucose : Low value ( 0- 40mg/dl)
  4. Chlorides : Marked decrease (600- 700 mg/dl)
  5. Proteins : High values (45-300 mg/dl)

Viral infection

  1. Appearance : Clear
  2. Cells/ Cumm (μL) :(10-200) mostly Lymphocytes
  3. Glucose : Slightly low or normal
  4. Chlorides : Moderate decrease
  5. Proteins :High values (45-300 mg/dl)

Fungal infection ( very rare)

  1. Appearance : Clear
  2. Cells/ Cumm (μL) : (0-5) lymphocyte
  3. Glucose : Low values (0-40 mg/dl)
  4. Chlorides : Normal or slight decrease
  5. Proteins : Normal

Acute purulent meningitis

  1. Appearance : Cloudy to purulent cloy
  2. Cells/ Cumm (μL) : Very high count (500-20000) per cumm mostly neutrophils
  3. Glucose : Very low values (0-40 mg/dl)
  4. Chlorides : Low values (600-700 mg/dl)
  5. Proteins : Very high (45 -1000 mg/dl) increase in globulins

Tuberculous meningitis

  1. Appearance : Cloudy, fibrin web
  2. Cells/ Cumm (μL) : High count (10-500mg/dl) mostly lymphocyte
  3. Glucose : Very low values (0-40 mg/dl)
  4. Chlorides : Very low values (500-600mg/dl)
  5. Proteins : High values (45-500 mg/dl), Increase in globulins

Acute Syphilitic meningitis

  1. Appearance : Clear or turbid
  2. Cells/ Cumm (μL) : High count (20-2000) mostly Lymphocytes
  3. Glucose : Low values (0-40 mg/dl)
  4. Chlorides : Normal or slightly decreased
  5. Proteins :Normal

Brain tumor

  1. Appearance : Clear or turbid
  2. Cells/ Cumm (μL) : High count (25-2000) mostly Lymphocytes
  3. Glucose : Low values (0-40 mg/dl)
  4. Chlorides : Normal or slightly decreased
  5. Proteins : Increased, globulin : increased

Cerebral hemorrhage

  1. Appearance : Xanthochromic
  2. Cells/ Cumm (μL) : 0 – 5
  3. Glucose : variable
  4. Chlorides : Normal
  5. Proteins : Increased, Globulin : Normal

Encephalitis Lethargic

  1. Appearance : Clear
  2. Cells/ Cumm (μL) : 10 – 100 all Lymphocyte
  3. Glucose : Slightly increased 80 – 120 mg/dl
  4. Chlorides : Normal
  5. Proteins : Normal or increased

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Specimen collection

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  • The specimen should be collected by a physician, a specially trained technician or nurse.
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  • The sterile lumber puncture needle is inserted between the 4th and 5th lumber vertebra to adapt of 4-5 cm.
  • After the withdrawal of stylet the fluid is collected throw the needle into two test tubes.
  • 1. Tube 1: (sterile tube) about 0.5 ml or few drops of CSF
  • 2. Tube 2. About 3 to 5 ml of CSF.
  • Important
  • 1. The specimen in tube no. 1 may be used for bacterial culture (if necessary) : Refer to Bacteriology Section for further details.
  • 2. Specimen in the second tube is centrifuged.
  • a) Supernatant is used for the biochemical test such as glucose, protein, globulin and chlorides.
  • b) Use the sediment for the following purposes.
  • i. Prepare 3 smears.
  • – Smear 1: for Gram’s staining
  • – Smear 2 : for Acid – fast staining
  • – Smear 3 : for differential leukocyte count
  • ii. Prepare weight mount for Trypanosoma
  • iii. Proceed for Indian ink preparation in case of cryptococcus infection.
Always remember
  1. The collected CSF specimen must be examined immediately (at least within 1 hours of the collection).
  2. The specimen collected for bacterial culture should not be stored in the refrigerator. (The commonly sought pathogen Neisseria meningitidis is killed by exposure to cold). The specimen meant for biochemical tests only, may be stored at 3-80C for 3 to 3 hrs.
  3. Cells and Trypanosomes are rapidly lysed after the collection of CSF. Hence urgent analysis if CSF is necessary.
  4. The specimen is difficult to collect, hence once it is collected it is necessary to analyze the specimen carefully and economically.
  5. The specimen may contain virulent organisms, hence it I’d necessary to handle it carefully.

Why Get CSF Tested?

To diagnose a disease or condition affecting the central nervous system such as meningitis, encephalitis, bleeding around the brain, cancer, or autoimmune disorder

When To Get CSF Tested?

When your health care provider suspects that your symptoms are due to a condition or disease involving your central nervous system

Sample Required?

A sample of cerebrospinal fluid (CSF) collected by a health care practitioner from the lower back using a procedure called a lumbar puncture or spinal tap

Test Preparation Needed?

You will be instructed to empty your bladder and bowels prior to sample collection. It will be necessary to lie still in a curled-up fetal position during the collection and to lie flat and still for a time period after the collection.

What is being tested?

Cerebrospinal fluid (CSF) is a clear, watery liquid that flows around the brain and spinal cord, surrounding and protecting them. CSF testing is performed to evaluate the level or concentration of different substances and cells in CSF in order to diagnose conditions affecting the brain and spinal cord (central nervous system).CSF is produced and secreted by the choroid plexus, a special tissue that has many blood vessels and that lines the small cavities or chambers (ventricles) in the brain. The total CSF volume is 3-5 ounces (90-150 mL) in adults and 0.3-2 ounces (10-60 mL) in newborns. CSF is continually produced, circulated, and then absorbed into the blood. About 17 ounces (500 mL) of CSF are produced each day. This rate of production means that all the CSF is replaced every few hours.A protective, semi-permeable barrier separates the brain from the bloodstream. This blood-brain barrier allows some substances to cross and prevents other substances from crossing. Importantly, it helps keep large molecules, toxins, and most blood cells away from the central nervous system. Any condition that disrupts this protective barrier may result in a change in the normal level or makeup of CSF. Because CSF surrounds the brain and spinal cord, testing a sample of CSF can be very valuable in diagnosing a variety of conditions affecting the central nervous system.Although a sample of CSF may be more difficult to obtain than, for example, urine or blood, the results of CSF testing may reveal more directly the cause of central nervous system conditions. The following are some examples:Meningitis, an infection of the layers that cover the brain and spinal cord (meninges), and encephalitis, an infection in the brainAutoimmune diseases that affect the central nervous system, such as multiple sclerosisCancers of the central nervous system or cancers that have spread to the central nervous system, such as leukemiaAlzheimer disease, an irreversible form of dementia.

When is it ordered?

CSF testing may be ordered when your health care practitioner suspects that you have a condition or disease involving your central nervous system. It may be ordered when:

  • You have suffered trauma to the brain or spinal cord
  • You have been diagnosed with cancer that may have spread into the central nervous system
  • Your medical history and/or signs or symptoms suggest a condition affecting your central nervous system. The signs and symptoms of central nervous system conditions can vary widely and many overlap with a variety of diseases and disorders. They may have sudden onset, suggesting an acute condition, such as central nervous system bleeding or infection, or may be slow to develop, indicating a chronic disease, such as multiple sclerosis or Alzheimer disease.

CSF testing may be ordered when you have some combination of the following signs and symptoms, especially when accompanied by flu-like symptoms that intensify over a few hours to a few days and fever:

  • Changes in mental status and consciousness
  • Sudden, severe or persistent headache or a stiff neck
  • Confusion, hallucinations or seizures
  • Muscle weakness or lethargy, fatigue
  • Nausea (severe or prolonged)
  • Sensitivity to light
  • Numbness or tremor
  • Dizziness
  • Difficulties with speech
  • Difficulty walking, lack of coordination
  • Mood swings, depression
  • Infants may be increasingly irritable, cry when they are held, have body stiffness, refuse food, and have bulging fontanels (the soft spots on the top of the head)

What other tests may be done in addition to CSF testing?

Other laboratory tests that may be ordered along with or following CSF testing include:Blood culture—to detect and identify bacteria or fungi in the bloodCulture and/or molecular testing of specimens collected from other possible sites of infection that led to meningitis or encephalitisBlood glucose, total protein—to compare with CSF glucose and protein levelsCBC (complete blood count)—to evaluate cell counts in bloodBlood tests (serologic testing) to detect proteins released from disease-causing microbes (pathogens) or antibodies against a variety of pathogens, such as West Nile Virus and other arbovirusesCRP (C-reactive protein)—this is the preferred test to detect inflammation. An ESR (erythrocyte sedimentation rate) may be done instead if CRP is not available.CMP (comprehensive metabolic panel)—a group of tests used to evaluate electrolyte balance and the health of your organs.


Cerebrospinal fluid (CSF) analysis is a group of laboratory tests that measure chemicals in the cerebrospinal fluid. CSF is a clear fluid that surrounds and protects the brain and spinal cord. The tests may look for proteins, sugar (glucose), and other substances.

Alternative Names

Cerebrospinal fluid analysis

How the Test is Performed

A sample of CSF is needed. A lumbar puncture, also called a spinal tap, is the most common way to collect this sample. Less common ways to take a fluid sample include:

  • Cisternal puncture
  • Removal of CSF from a tube that is already in the CSF, such as a shunt, ventricular drain, or pain pump
  • Ventricular puncture

After the sample is taken, it is sent to the laboratory for evaluation.

Your doctor will ask you to lie flat for at least one hour after the lumbar puncture. You may develop a headache after the lumbar puncture. If it happens, drinking caffeinated beverages such as coffee, tea or soda may help.

How to Prepare for the Test

Your health care provider will tell you how to prepare for lumbar puncture.

Why the Test is Performed

Analysis of CSF can help detect certain conditions and diseases. All of the following can be, but are not always, measured in a sample of CSF:

  • Antibodies and DNA of common viruses
  • Bacteria (including that which causes syphilis, using a VDRL test)
  • Cell count
  • Chloride
  • Cryptococcal antigen
  • Glucose
  • Glutamine
  • Lactate dehydrogenase
  • Oligoclonal banding to look for specific proteins
  • Myelin basic protein 
  • Total protein
  • Whether there are cancerous cells present
  • Opening pressure 

Normal Results

Normal results include:

  • Antibodies and DNA of common viruses: None
  • Bacteria: No bacteria grows in a lab culture
  • Cancerous cells: No cancerous cells present
  • Cell count: less than 5 white blood cells (all mononuclear) and 0 red blood cells
  • Chloride: 110 to 125 mEq/L (110 to 125 mmol/L)
  • Fungus: None
  • Glucose: 50 to 80 mg/dL or 2.77 to 4.44 mmol/L (or greater than two-thirds of blood sugar level)
  • Glutamine: 6 to 15 mg/dL (410.5 to 1,026 micromol/L)
  • Lactate dehydrogenase: less than 40 U/L
  • Oligoclonal bands: 0 or 1 bands that are not present in a matched serum sample
  • Protein: 15 to 60 mg/dL (0.15 to 0.6 g/L)
  • Opening pressure: 90 to 180?mm of water
  • Myelin basic protein: Less than 4ng/mL

Normal value ranges may vary slightly among different laboratories. Talk to your provider about the meaning of your specific test results.

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

What Abnormal Results Mean

An abnormal CSF analysis result may be due to many different causes, including:

  • Cancer
  • Encephalitis (such as West Nile and Eastern Equine)
  • Hepatic encephalopathy
  • Infection
  • Inflammation
  • Reye syndrome
  • Meningitis due to bacteria, fungus, tuberculosis, or a virus
  • Multiple sclerosis (MS)
  • Alzheimer disease
  • Amyotrophic lateral sclerosis (ALS)
  • Pseudotumor Cerebrii
  • Normal pressure hydrocephalus

This article written by Madan Singh (Technical assistance, department of Biochemistry, All India Institute of Medical Sciences, Raipur, CG.)

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