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In addition to chemistry tests, such as protein and glucose, other routine tests may be performed to look for microorganisms if meningitis or encephalitis is suspected.
CSF gram stain for direct observation of microorganisms under a microscope. A sample of CSF is centrifuged and the concentrated portion is placed on a slide and treated with a special stain for examination under the microscope. There should be no microorganisms in CSF fluid. If or are present on a CSF gram stain, then the patient has bacterial or fungal meningitis or encephalitis.
CSF culture and sensitivity is used to detect any microorganisms, which will grow in the . If bacteria are present, they can be tested in the laboratory to predict the best choices for antimicrobial therapy for the affected person and prophylaxis (preventive treatment) of close contacts, if needed. If there are no microorganisms present, it does not rule out an infection; they may be present in small numbers or unable to grow in culture due to prior antibiotic therapy. Some amebae, single cell parasites, may also be detected with a culture.
If any of the initial tests are abnormal or if the doctor strongly suspects a central nervous system infection, then additional testing may be ordered. This may include one or more of the following:
Detection of viruses – detection of viral genetic material (DNA, RNA) by polymerase chain reaction (PCR) testing; for example, herpes virus and enteroviruses. Positive PCR tests for viral DNA or RNA, antigen tests, and growth on viral cultures indicate that a person has a viral infection and may have viral encephalitis or meningitis. The presence of viral and their increase over time indicates a recent infection by that virus (such as a four-fold increase in the of West Nile Virus antibody in samples drawn several weeks apart).
CSF Cryptococcal antigen – to detect a fungal infection caused by the yeast Cryptococcus neoformans
Other CSF antigen tests – depending on which organism(s) are suspected
Specific CSF antibody tests – depending on which organism(s) are suspected
Other CSF tests for infectious diseases that are less commonly ordered include:
CSF AFB smear and culture may be positive with tuberculosis and with other mycobacteria
CSF molecular tests for Mycobacteria tuberculosis when tuberculosis is suspected
CSF syphilis testing (VDRL) positive with neurosyphilis (involvement of the brain by syphilis); a negative does not rule out brain involvement