Medical Health Encyclopedia

Blood tests may be used to determine blood counts, blood sugar levels, liver function, and blood clotting factors. Urine samples may also be taken.

Serum Antibody Tests for Acute Viral Encephalitis

An arbovirus can be isolated only within the first 2 to 4 days of the attack, so methods for directly detecting it in blood or cerebrospinal fluid samples are rarely successful.

In surviving patients, tests may be conducted using a clear fluid called serum, which can be derived from blood, cerebrospinal fluid, or other fluids. Such tests may identify many of the viruses by detecting specific antibodies against them in the serum. Antibodies are factors produced by the immune system to fight specific organisms and other infections. They remain in the system after the organism or infection has gone.

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Tests for antibodies are only useful in patients who survive the acute attack. They must be performed at the following times:

• The first test is taken when the symptoms first occur. At that time, antibody levels are low or absent. Antibodies rise over time.
• The next test is taken during convalescence (about 3 to 5 weeks later). For a diagnosis of the virus, antibody levels at that time should be at least four times the initial measurement.

In the case of West Nile virus, a 2003 study suggested that antibodies may persist a year or more after an initial infection.

Polymerase Chain Reaction (PCR)

A test called the polymerase chain reaction (PCR) is a rapid diagnostic test that is used to detect some viruses:

• PCR uses blood, spinal fluid, or any other tissue specimen that may contain the virus.
• It replicates a piece of the viral DNA millions of times until the virus is detectable, usually within 2 or 3 hours.
• Sensitivity is almost equal to viral culture and results are much quicker.