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CSF chemistry
CSF chemistry

CSF chemistry
Definition:
This test is a fluid analysis of cerebral spinal fluid (CSF). CSF is the fluid that bathes, cushions, and protects the brain and spinal cord. It flows through the skull and spine in the subarachnoid space, which is the area immediately surrounding the brain. CSF chemistry refers to the analysis of the fluid to look for things, such as protein and glucose content, as well as other components, which can often help in diagnosing disease.

Alternative Names:
Chemistry - CSF

How the test is performed:

A lumbar puncture (spinal tap) is the most common means of collecting a specimen of CSF. You are positioned on your side with your knees curled up to your abdomen and your chin tucked in to your chest. (Occasionally this procedure is performed with the person sitting bent forward). The skin is scrubbed, and a local anesthetic is injected over the lower spine.

The spinal needle is inserted, usually between the 3rd and 4th lumbar vertebrae. Once the needle is properly positioned in the subarachnoid space, pressures can be measured and fluid can be collected for testing. After the sample is collected, the needle is removed, the area is cleaned, and a bandage is applied. You will be asked to remain flat, or nearly flat, for 6 to 8 hours after the test. A lumbar puncture with fluid collection may also be part of other procedures, particularly a myelogram (X-ray or CT scan after dye has been inserted into the CSF).

Alternative methods of obtaining CSF are rarely used, but they may be recommended if you have a problem, such as lumbar deformity or infection, which would make lumbar puncture impossible or unreliable. Cisternal puncture involves insertion of a needle below the occipital bone (back of the skull). It can be hazardous because the needle is inserted close to the brain stem. Ventricular puncture is even more rare, but may be indicated when sampling of CSF is necessary in people with possible impending brain herniation. It is usually performed in the operating room. A hole is drilled in the skull and a needle is inserted directly into the lateral ventricle of the brain.

The CSF is then taken to the laboratory for evaluation.
How to prepare for the test:
Be prepared to sign a consent form, and to remain in the hospital for at least the 6 to 8 hours after the test that you must remain flat.

If your child is to have this test performed, it may be helpful to explain how the test will feel, and even practice or demonstrate on a doll. The more familiar your child is with what will happen, and why, the less anxiety he or she will feel.
How the test will feel:
The curled position may be uncomfortable, but you must remain in the it to avoid moving the needle and possibly injuring the spinal cord.

The scrub will feel cold and wet. The anesthetic will sting or burn when first injected. There will be a hard pressure sensation when the needle is inserted, and there is usually some brief pain when the needle goes through the meninges. This pain should stop in a few seconds. Overall, discomfort is minimal to moderate. The entire procedure usually takes about 30 minutes, but may take longer. The actual pressure measurements and fluid collection only takes a few minutes.
Why the test is performed:
This test is performed to evaluate the following. (For information on abnormal values, please see the specific test if indicated. If not indicated, please see the abnormal values section in this article):
Normal Values:
  • cell count: less than 0 to 5 white blood cells (WBC) and 0 red blood cells (RBC)
  • culture and sensitivity: no organism growth
  • protein: 15 to 45 mg/dl
  • glucose: 50 to 80 mg/100 ml
  • serology for syphilis: no presence of antibodies
  • fungus: no presence of fungus
  • immunofixation: one or less bandings
  • glutamine: 6 to 15 mg/dl
  • lactate dehydrogenase: less than 2.0 to 7.2 U/ml
  • chloride: 700 to 750 mg/dl
  • cytology: no malignant cells present
Note:
  • mg/dl = milligrams per deciliter
  • U/ml = units per milliliter
  • mg/ml = milligrams per milliliter
What abnormal results mean:
  • Abnormal glutamine results may indicate:
  • Elevated lactate dehydrogenase levels may indicate:
    • inflammation or infection
  • Increased protein may suggest inflammation
  • Decreased glucose may mean meningitis due to bacteria, fungus or tuberculosis
  • Increased white blood cells may mean an infection or another inflammatory process
  • Cytology is sent to look for evidence of malignant cancer cells
What the risks are:
Cisternal puncture or ventricular puncture carries additional risk of damage to the brainstem or brain tissue and risk of bleeding within the brain, resulting in incapacitation or death.
Review Date: 5/12/2001
Reviewed By: Galit Kleiner-Fisman, M.D., Department of Neurology, Beth-Israel Deaconess Medical Center, Boston, MA. Review provided by VeriMed Healthcare Network.
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