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% of people with the infection
don't have any symptoms. But the WNV can cause:
Nausea and vomiting
Swollen lymph nodes
Other symptoms, which are rare, include:
If you're infected with WNV, your immune system makes antibodies against it. These
antibodies are designed to destroy the virus. The WNV antibody test looks for these
antibodies in your blood. If you have them, it means you have an infection.
Why do I need this test?
You may need this test if your healthcare 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 getting a blood
transfusion or donated organ. Nursing or pregnant women may also need the test if
their healthcare provider 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
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 healthcare
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 means 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
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
Diet, medicines, 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 healthcare provider to be sure.