Cerebrospinal Fluid (CSF) Analysis: Common Questions

CSF is a major fluid in the body. It is produced by the choroid plexus of the two lateral ventricles.
It provides nutrients to the nervous tissue, removes metabolic waste and acts as protective barrier to prevent trauma of the brain and the spinal cord.

a. Adults: 90-150 ml
b. Neonates :10-60 ml

It is collected by using lumbar puncture needle inserted at the level of L3/4 or L4/5 interspace..

The material has to be withdrawn slowly specially during elevated CSF pressure, it requires monitoring of the pressure.

The fluid has to be ideally collected in three tubes and collected in the order in which it is withdrawn.
a. 1st container: for chemical and serological tests
b. 2nd container: for microbiologic examination
c. 3rd container : for cell count.

The appearance of the fluid immediately after collection gives valuable information listed as below
a. Clear: indicates normal
b. Turbid : indicates inflammatory process like meningitis
c. Bloody: may be due to hemorrhage or traumatic tap
d. Xanthochromic: may indicate old hemorrhage or elevated Bilirubin levels or sometimes even the presence of increased proteins
e. Clotted : indicates clotted blood or any disorder of blood brain barrier where fibrinogen is introduced into the fluid.

If it is cerebral hemorrhage, the blood will be evenly distributed in all the three containers, whereas if it is traumatic tap, it is concentrated more in the first container and reduces in subsequent containers.

It is done by using a Neubaur counting chamber with a diluted or undiluted fluid. If it is a hemorrhagic fluid, then the diluting fluid will be 3 % glacial acetic acid.

The cerebrospinal fluid should be centrifuged and smears are prepared. The differential count is done on a stained smear.

Lymphocytes and Monocytes are the normal cells found in cerebrospinal fluid.adults have predominantly lymphocytes where as children have predominantly Monocytes..

Increase in the number of normal cells in the cerebrospinal fluid is called pleocytosis.

a. Lymphocytes: are seen in normal as well as tubercular and viral meningitis
b. Neutrophils: predominantly in bacterial meningitis. Also can be seen early stages of other meningitis. Can be seen in hemorrhagic tap
c. Monocytes: are normally found as well as in viral and tubercular meningitis
d. Macrophages : indicate old hemorrhage
e. Abnormal cells like blasts are seen in acute leukemias and malignant cells in various primary and metastatic neoplasms..

The normal levels of protein in cerebrospinal fluid is 15-45mg/dl

a. Increased protein: seen in meningitis, hemorrhage, diabetes, neurosyphilis
b. Decreased protein levels: can be due to rapid production of cerebrospinal fluid or water intoxication.

The normal levels of glucose is 60 to 70% of the plasma glucose levels.

a. Increases when the plasma glucose levels increases
b. Decreases in bacterial meningitis..

The role is identification of causative agents in meningitis. This is usually done by CSF culture.

Increased levels of glutamine is usually associated with some disturbance in consciousness. Usually done in patients with coma of unknown cause. It is also increased in children with Reye syndrome.

The serologic tests are performed to detect the presence of neurosyphilis. VDRL test for syphylis is usually done.

	Bacterial	Viral	Tubercular	Fungal
Appeareance	Cloudy or purulent	Clear	Clear or opaque. Cob web may be formed	Clear or slightly cloudy
Pressure	Elevated	Normal or elevated	Normal or elevated	elevated
WBC count	Elevated >1000/microliter	Elevated 10-100/microliter	Elevated 10-1000/microliter	Elevated 10-1000/microliter
Type of WBC	Neutrophils	Neutrophils in early stages. Lymphocytes later	Lymphocytes and monocytes	Lymphocytes and monocytes
Proteins	Markedly increases	Moderately increases	Marked	Marked
Glucose	Markedly reduced	Normal	Mildly reduced	Normal to reduced
Culture	Positive for bacteria	Negative	Positive for tuberculosis	Fungal positive