What it measures
Antibodies to West Nile virus, which is spread by mosquito bites in parts of Europe, Africa, the Middle East, Asia and the Americas. IgM antibodies point to a recent infection; IgG antibodies show infection at some point. Most infections cause no symptoms.
Why people test it
- Tested after a fever, headache or rash following travel to an area with West Nile virus.
- Used to look for a past infection after an illness abroad.
Typical range
Reported as positive, negative or equivocal for each antibody type; antibodies to related viruses, such as dengue, Zika or the yellow fever vaccine, can cross-react. Methods and cut-offs vary between labs, and your report shows how the lab reads the result.
Finger-prick or vein?
Offered as a vein draw only.