Laboratory screening of blood, urine, and body secretions can help detect and identify brain and/or spinal cord infection and determine the presence of antibodies and foreign proteins. Such tests can also rule out metabolic conditions that have similar symptoms.
For example, a throat culture may be taken to check for viral or bacterial organisms that cause meningitis or encephalitis. In this procedure, the back of the throat is wiped with a sterile cotton swab, which is then placed on a culture medium. Viruses and bacteria are then allowed to grow on the medium. Samples are usually taken in the physician's office or in a laboratory setting and sent out for analysis to state laboratories or to the U.S. Centers for Disease Control and Prevention. Results are usually available in two to three days.
Analysis of the cerebrospinal fluid that surrounds and protects the brain and spinal cord can detect infections in the brain and/or spinal cord, acute and chronic inflammation, and other diseases.
In a procedure known as a spinal tap (or lumbar puncture), a small amount of cerebrospinal fluid is removed by a special needle that is inserted into the lower back. The skin is anesthetized with a local anesthetic prior to the sampling. The fluid, which is completely clear in healthy people, is tested to detect the presence of bacteria or blood, as well as to measure glucose levels (a low glucose level is a sign of bacterial or fungal meningitis) and white blood cells (elevated white blood cell counts are also a sign of infection). The procedure is usually done in a hospital and takes about 45 minutes.
Computer-assisted imaging can reveal signs of brain inflammation, internal bleeding or hemorrhage, or other brain abnormalities. Two painless, noninvasive imaging procedures routinely used to make an encephalitis diagnosis are CT scans and MRI.