West Nile Virus Testing
If you have symptoms of West Nile virus infection, your doctor may recommend West Nile virus testing. The most commonly used laboratory test for diagnosing the virus measures the antibodies that you produce. The test may not be positive when symptoms of West Nile virus first occur, but is usually positive in infected people within 8 days of the onset of symptoms.
In order to make a diagnosis of West Nile virus, your doctor will ask a number of questions, perform a physical exam, and recommend certain tests. As part of diagnosing a West Nile virus infection, the doctor will also rule out other causes of possible West Nile virus symptoms.
If your doctor determines that you are at high risk and have symptoms of West Nile encephalitis, he or she will draw a blood sample and send it to a commercial or public health laboratory for confirmation.
The most commonly used laboratory test for diagnosing West Nile virus measures antibodies that are produced by the infected person at a very early stage of the infection. These antibodies, called IgM antibodies, can be measured in blood or cerebrospinal fluid (CSF), which is the fluid surrounding the brain and spinal cord. This blood test may not be positive when symptoms of West Nile virus first occur; however, the test is positive in most infected people within 8 days of the onset of symptoms.