West Nile Virus Antibody (Blood)

Does this test have other names?


What is this test?

This is a blood test that checks for West Nile virus (WNV). This is a viral infection that usually affects birds. The virus spreads when a mosquito bites an infected bird and then bites a human. An infected mother may pass the virus along to her fetus during pregnancy or to her infant during breastfeeding. Some people may get the virus from infected blood or organs.

WNV is most common during the summer and fall. About 80 percent of people with the infection don't have any symptoms, but the WNV can cause:

  • Nausea and vomiting

  • Headaches

  • Body aches

  • Swollen lymph nodes

  • Skin rash

Other symptoms, which are rare, include:

  • Muscle weakness

  • Vision loss

  • Stiff neck and headache

  • High fever

  • Confusion or disorientation

  • Tremors or convulsions

  • Coma

  • Paralysis

  • Numbness

If you're infected with WNV, your immune system produces antibodies against it. These antibodies are designed to destroy the virus. The WNV antibody test looks for these antibodies in your blood, which indicate infection. 

Why do I need this test?

You may need this test if your health care provider suspects that you have WNV. These are reasons you may have WNV:

  • You have been bitten by a mosquito.

  • You show symptoms of WNV.

  • You have touched a dead bird.

You may need to be tested if you show symptoms of the virus after receiving a blood transfusion or donated organ. Nursing or pregnant women may also need the test if their doctor suspects they may have WNV.

Most people don't need treatment for WNV – only those with very serious symptoms. 

What other tests might I have along with this test?

The WNV test usually requires a blood sample. People with severe symptoms may also need to give a sample of cerebrospinal fluid or a small sample of body tissue for testing.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

A normal, or negative, test result shows that you have no antibodies to the WNV in your blood. A positive test result shows antibodies to the virus, which indicates that you have the infection.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm. 

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Getting the test too soon after infection may affect your results. For best results, the test should be done at least a week after you suspect infection. If the antibodies haven't had time to show up in your blood, test results may be negative even if you have WNV.

Diet, medications, and lifestyle habits should not change the presence of WNV antibodies in your blood.

How do I get ready for this test?

A blood test rarely requires any preparation. You can probably eat, drink, and take your medication as usual, but check with your doctor to be sure.