Which lab tests are used in the diagnosis of viral meningitis?

Updated: Jul 17, 2018
  • Author: Cordia Wan, MD; Chief Editor: Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM  more...
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Routine chemistry and hematology tests should be performed.

In neonatal and severe cases of viral meningitis, arterial blood gas analysis, coagulation studies, and liver function tests should also be considered.

The serum white blood cell (WBC) count is not a sensitive indicator of the severity of infection, especially in the immunocompromised, neonatal, or elderly patient.

The serum sodium level may be abnormal because of dehydration or the rare occurrence of syndrome of inappropriate antidiuretic hormone secretion (SIADH).

The serum amylase level may be elevated in cases of viral meningitis that are caused by mumps, even in the absence of parotitis.

Reports have shown high C-reactive protein (CRP) levels in the serum of children with bacterial meningitis whose CSF Gram stain findings were negative for bacteria. However, a comparable group of children with viral meningitis did not have similar elevations in serum CRP (ie, 50-150 in bacterial meningitis group vs < 20 in the viral meningitis group).

All patients whose condition is not improving clinically within 24-48 hours should have a more extensive workup to discern the cause of meningitis.

Blood, feces, and throat swabs may be sent for viral serology and cultures.

Acid-fast staining of CSF should be performed, and the remaining fluid should be sent for testing, using the polymerase chain reaction (PCR), for HIV and CMV. [8]

Serum titers of antibodies against HIV and toxoplasma should be obtained.

Additional serum collection 10-21 days later may aid in discerning rising titers in the antibodies against specific viral pathogens; a 4-fold increase in viral antibodies confirms the diagnosis. This is particularly useful for arboviral and LCMV cases, but it also is helpful in ruling out toxoplasmosis, leptospirosis, borreliosis, and rickettsial infections. Although some of these studies do not yield an immediate result for clinical decision making, they may be useful for prognostication.

In patients in whom encephalitis is suspected, MRI with contrast enhancement and adequate visualization of the basal frontal and temporal areas is necessary

Electroencephalography (EEG) may be performed if encephalitis or subclinical seizures are suspected in the altered patient. Periodic lateralized epileptiform discharges (PLEDs) are often seen in herpetic encephalitis.

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