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Direct immunofluorescence (DFA), indirect immunofluorescence (IFA) antibody staining.
This test checks for influenza antibodies in a sample of secretions from your nose or throat.
Influenza is a common illness of the respiratory system. It can have serious health effects or even be fatal, especially if you have a weakened immune system.
Influenza A is more common and can be more serious. It spreads easily through water droplets in the air, and often affects many people at the same time during fall and winter.
Healthcare providers can test for influenza, or the "flu," in several ways. One method uses nasal washes and throat swabs to look for influenza antigens. Results are usually known quickly, in less than 30 minutes. The method described in this test is immunofluorescence. It uses a staining technique to look for influenza antibodies. Results may be available in 1 to 4 hours. Results from these rapid testing methods are not as accurate as conventional viral cultures—another type of influenza test—but are commonly used as initial screening tests. Viral cultures may take from three to10 days to yield results.
You may need this test if your healthcare provider suspects that you have the flu. Symptoms of the flu include:
Weakness or tiredness
Runny or stuffy nose
Pain in the muscles around the eyes or blurred, teary vision
Vomiting or diarrhea
Symptoms of the flu often appear suddenly, about 1 to 2 days after you are infected. Your body often fights off an influenza infection within a few days, but some people develop severe pneumonia or other serious complications.
Even if you do not have immediate signs of infection, you should be tested during flu season or an influenza outbreak if you:
Were discharged from a hospital and got a sudden fever or respiratory illness
Are in the hospital and have a fever or respiratory illness
Your healthcare provider may also order other tests, including a viral culture, rapid antigen tests, or reverse transcriptase polymerase chain reaction test.
Testing for influenza antibodies is considered a screening test. Your healthcare provider may use more accurate tests if he or she thinks that the diagnosis needs to be confirmed.
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 provider.
Normal results are negative, meaning 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 considered a true positive if other cases of influenza have been reported in your area at the time you're tested. It's possible to get a false-positive result, meaning that you are not really infected. Your healthcare provider may do more tests if needed.
This test requires a sample of mucus or other respiratory secretions. Your healthcare provider will use a sterile swab to collect a sample from inside your nose or throat.
Another method of doing this test requires a nasopharyngeal aspirate, or NPA. In this procedure, your healthcare provider will inject saline solution and collect a sample through your nose.
This test does not pose any serious risks. You may feel discomfort or gagging sensations when your throat or nasal cavity is swabbed. Collecting an NPA may also be uncomfortable.
Other respiratory infections may cause a false-positive result. Influenza screening tests are sometimes inaccurate, so a negative test result should be interpreted with caution.
You don't need to prepare for this test.
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