CSF chemistry
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 substances (for information on abnormal values, please see the specific test if indicated; if not indicated, please see the abnormal values section in this text):
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