From the Guidelines
A cerebrospinal fluid (CSF) test for diagnosing viral meningitis or encephalitis involves a lumbar puncture procedure followed by laboratory analysis of the collected fluid, including viral tests such as polymerase chain reaction (PCR) and antibody testing, as recommended by the Infectious Diseases Society of America 1. The procedure typically involves a doctor inserting a thin needle between vertebrae in the lower back to collect CSF from around the spinal cord. The patient lies on their side in a curled position or sits leaning forward to widen the spaces between vertebrae. After cleaning and numbing the area, the doctor collects about 1-4 teaspoons of fluid in sterile vials. The collected CSF undergoes several tests, including:
- Cell count
- Glucose and protein measurements
- Specific viral tests, such as:
- PCR testing to identify viral genetic material from herpes simplex virus, enterovirus, varicella-zoster virus, and other potential pathogens
- Antibody testing to detect virus-specific IgM in CSF, which is usually indicative of CNS disease
- Viral culture or next-generation sequencing in complex cases Results typically take 24-72 hours, though PCR results may be available sooner. The procedure carries small risks, including headache, bleeding, or infection, but these are uncommon with proper technique. This comprehensive CSF analysis is essential for distinguishing viral infections from bacterial or fungal causes, which require different treatments, as highlighted in the guidelines by the UK Joint Specialist Societies 1 and the Association of British Neurologists and British Paediatric Allergy, Immunology and Infection Group 1. In cases where viral meningitis is suspected, the CSF should be tested for enteroviruses, herpes simplex viruses type 1 and 2, and varicella zoster virus by PCR, and stool and/or throat swabs should be tested for enterovirus by PCR, as recommended by the UK Joint Specialist Societies guideline 1.
From the Research
CSF Test Overview
A cerebrospinal fluid (CSF) test is a diagnostic tool used to evaluate various conditions affecting the central nervous system, including viral meningitis or encephalitis. The test involves collecting a sample of CSF through a lumbar puncture, which is then analyzed for various parameters.
Parameters Analyzed
The following parameters are typically analyzed in a CSF test:
- Pressure
- Cell count and white cell differential
- Glucose and protein levels
- Gram's stain
- Culture
- Viral tests, such as polymerase chain reaction (PCR) or serology for specific viruses like enterovirus, herpes simplex, or varicella-zoster 2, 3
Viral Test
A viral test is used to diagnose viral meningitis or encephalitis. The test may involve:
- PCR to detect viral DNA or RNA in the CSF 3, 4
- Serology to detect antibodies against specific viruses in the serum or CSF 2, 3
- Measurement of interferon-alpha (IFN-alpha) levels in the serum or CSF, which can indicate a viral infection 3
Interpretation of Results
The results of the CSF test and viral test are interpreted together to diagnose viral meningitis or encephalitis. A diagnosis of viral meningitis is typically made based on a combination of clinical presentation, CSF analysis, and viral test results 2, 5. The presence of a specific viral agent in the CSF or serum can confirm the diagnosis and guide treatment decisions 2, 3.
Key Findings
Studies have shown that:
- Viral meningitis is a common cause of aseptic meningitis, with enterovirus and varicella-zoster being the most common etiological agents 3
- PCR and serology are useful diagnostic tools for detecting viral infections in the CSF 3, 4
- The under-utilization of available diagnostic tests, including PCR and serology, can lead to a significant proportion of patients remaining without a diagnosis 4 6, 5