A cerebral spinal fluid test is an analysis performed on the fluid around the spinal cord and brain. Doctors extract the fluid through a lumbar, cisternal, or ventrictular puncture. Once the cerebrospinal fluid (CSF) is collected, a laboratory can perform various tests to diagnose central nervous system disorders or problems, such as multiple sclerosis, Guillain-Barre syndrome, meningitis, encephalitis, bleeding in the brain or spinal cord, or cancerous tumors.
A lumbar puncture, or spinal tap, is the most common method to extract fluid for a cerebral spinal fluid test. The patient bends forward to expose his spine or lies down on his side with his knees curled up toward his chest. The doctor usually numbs the lower back with an anesthetic injection before piercing the lower back area to collect a small sample of cerebrospinal fluid.
In rare cases, a doctor may need to collect the fluid from the skull area due to severe injury to the lower back or brain herniation, a condition where the brain and cerebrospinal fluid are pushed out of their normal positions, usually due to trauma. A cisternal puncture collects fluid from the base of the skull for a cerebral spinal fluid test. It is performed with a special x-ray to help the doctor determine where to guide the needle, since the base of the skull is so close to the brain stem. A ventricular puncture involves collecting the cerebrospinal fluid from a hole drilled into the skull if the doctor suspects a brain herniation, though this is very rare.
Doctors and laboratory analysts usually first look at the fluid in comparison to water during a cerebral spinal fluid test. Changes in the color and consistency of the fluid, which is normally clear with the same consistency as water, can indicate bleeding or point to bacterial infections or cancer. The doctor may also test for the amount of protein in the fluid. Increased levels of protein can point to syphilis, multiple sclerosis, meningitis, tumors in the spinal cord or brain, or Guillain-Barre syndrome.
Other common tests performed on cerebrospinal fluid include chemical tests to detect certain proteins and other substances to help doctors accurately diagnose a patient. For example, if meningitis is suspected, a doctor may order a test to measure the level of lactic acid in the fluid to help determine whether the infection is bacterial or viral. Other tests search for specific bacteria, viruses, and other microorganisms.