This blood test checks for antibodies that develop when you have the 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:
Stiff neck and headache
Confusion or disorientation
Tremors or convulsions
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.
You may need this test if your healthcare provider suspects that you have WNV because:
You have been bitten by a mosquito.
You show symptoms of WNV.
You have touched a dead bird.
You may also need to be tested if you show symptoms of the virus after getting a blood transfusion or donated organ. Nursing or pregnant women may 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.
The WNV test usually is done with a blood sample. People with severe symptoms may also need to have a sample of cerebrospinal fluid or a small sample of body tissue tested.
Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you.
The test is done with a blood sample, which is drawn through a needle from a vein in your arm.
Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore.
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, medicines, and lifestyle habits should not affect the results of the test.
A blood test rarely needs any preparation. Always check with your healthcare provider. Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you take. This includes medicines that don't need a prescription and any illegal drugs you may use.