Rapid influenza diagnostic test, RIDT
This test quickly checks for signs of the influenza viruses A and B in a sample of secretions from your nose or throat.
Influenza—or the "flu"—is an illness of the respiratory system. Influenza A is more common than influenza B. It spreads easily through water droplets in the air from coughs or sneezes of people who are infected. It often affects many people at the same time during fall and winter.
Symptoms of the flu often show up suddenly. This is about 1 to 4 days after you are infected. Most people will get better within a few days to less than 2 weeks. But those with a weakened immune system may get severe pneumonia or other serious problems.
Your healthcare provider can test for the flu in several ways. The rapid influenza antigen test usually gives results quickly. Immunofluorescence is another test that may be used. This test uses a staining technique. Results from these tests are not as accurate as viral cultures. But these tests are faster and easier and are commonly used for the first screening.
You don't always need an influenza test for your provider to diagnose the flu. Healthcare providers may make the diagnosis and begin treatment based on your symptoms and a physical exam.
You may need this test if you have symptoms of the flu to find out whether you have it. Symptoms of the flu include:
Weakness or tiredness
Runny or stuffy nose
Pain around your eyes or blurred vision
Vomiting or diarrhea
Even if you don't have symptoms, you may need this test 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
You may also need other tests. These include an immunofluorescence antibody test, viral culture, or reverse transcriptase polymerase chain reaction test for influenza DNA. Testing for influenza antigens is considered a screening test. Your healthcare provider may use more accurate tests if they think the diagnosis needs to be confirmed.
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.
A negative result means that no signs of the virus were found and that you may not have the flu. The results of this test should be interpreted with caution because rapid influenza antigen tests may have a significant number of false-negative results. This means that you may have the flu even if your results were negative.
A positive result means that signs of the virus were found and that you may have the flu, especially if other cases of the flu have been reported in your area at the time you are tested.
It's possible to get a false-positive result, meaning that you aren't really infected. You may need more tests to confirm this. Your healthcare provider may also treat you even if you have a negative test result.
This test requires a sample of mucus or other secretions from your nose or throat. Your healthcare provider will use a sterile swab to collect the sample.
Another way of taking a sample requires a nasopharyngeal aspirate (NPA). In this procedure, a healthcare provider will inject saline solution into your nose and then collect the sample.
You may feel discomfort or gagging when your throat or nasal cavity is swabbed. Collecting an NPA may also be uncomfortable.
If you have another respiratory infection, you may get a false-positive result.
You don't need to prepare for this test. Be sure your healthcare provider 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.