Antibody to West Nile Virus, IgM (Serum/Plasma)

Why This Test Is Done

Your healthcare provider may order this test if you have symptoms like fever, headache, body aches, or neurological issues (such as confusion, weakness, or seizures) that could be linked to West Nile virus infection, especially after exposure to mosquitoes in endemic areas. It may also be used during outbreaks or in high-risk groups like older adults or those with weakened immune systems.

What to Expect Before the Test

No special preparation is needed. You’ll typically have a small needle inserted into your arm to draw blood. If you’re concerned about needles, let your healthcare provider know so they can offer alternatives.

What the Test Results Mean

Positive results indicate recent infection with West Nile virus. Negative results mean no detectable IgM antibodies at the time of testing, but this doesn’t rule out past infection. Follow-up testing may be needed if symptoms persist or worsen.

Possible Side Effects or Risks

The most common side effect is mild bruising, redness, or soreness at the injection site. Rarely, you might experience fainting or dizziness after the blood draw. If you experience severe pain or swelling, contact your healthcare provider.