Does this test have other names?

Direct immunofluorescence (DFA), indirect immunofluorescence antibody staining

What is this test?

This test checks for flu (influenza) antibodies in fluid from your nose or throat.

The flu is a common illness of the respiratory system. It can have serious health effects. It can even cause death, especially if you have a weak immune system.

Influenza A is more common and can be more serious. It spreads easily through fluid droplets in the air. It often affects many people at the same time during the fall and winter months.

Doctors can test for influenza in several ways. One method uses nasal washes and throat swabs to look for influenza antigens. Results are shown quickly, in less than 30 minutes. The test described here uses immunofluorescence. This is a staining method to look for influenza antibodies. Results may be available in 1 to 4 hours. Results from a rapid testing method are not as accurate as a type of influenza test called a viral culture. But a rapid test is often used as a first screening test. A viral culture may take from 3 to10 days to show results.

Why do I need this test?

You may need this test if your doctor thinks that you may have the flu. Symptoms of the flu include:

• Fever.

• Headache.

• Muscle pain.

• Weakness or tiredness.

• Chills.

• Runny or stuffy nose.

• Cough.

• Sore throat.

• Pain in the muscles around the eyes or blurred, teary vision.

• Vomiting or diarrhea.

Symptoms of the flu often appear about 1 to 2 days after you are infected. The symptoms may feel severe right away. Your body may fight off an influenza infection within a few days. But some people develop severe pneumonia or other serious problems.

Even if you don't have signs of infection, you should be tested during flu season or an influenza outbreak if you:

• Were discharged from a hospital and have a sudden fever or respiratory illness

• Are in the hospital and have a fever or respiratory illness

What other tests might I have along with this test?

Testing for influenza antibodies is a screening test. This means you may need other tests that are more accurate to confirm your diagnosis. These tests may include: 

• Viral culture.

• Rapid antigen test.

• Reverse transcriptase polymerase chain reaction test.

What do my test results mean?

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your doctor what your test results mean for you.

A negative result means that no influenza antibodies were found and you likely don't have the flu.

A positive result means that you do have influenza antibodies. A positive result is more likely to be accurate with this test if other cases of influenza have been reported in your area. It's possible to get a false-positive result. This means that you are not really infected with the flu. Your doctor may do more tests if needed.

How is this test done?

This test is done with a sample of mucus or other fluid from your respiratory system. Your doctor will wipe a sterile swab inside your nose or throat.

Another method of doing this test is done with a nasopharyngeal aspirate (NPA). For this, your doctor will put saline solution in your nose and collect a sample.

Does this test pose any risks?

This test does not pose any serious risks. You may feel discomfort or gag when your throat or nasal cavity is swabbed. An NPA may also cause some discomfort.

What might affect my test results?

Other respiratory infections may cause a false-positive result. Influenza screening tests are sometimes not accurate.

How do I get ready for this test?

You don't need to prepare for this test. Be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don’t need a prescription and any illegal drugs you may use.