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 and can be more serious 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 appear suddenly, about 1 to 4 days after you are infected. Most people will recover from the flu within a few days to less than 2 weeks, but those with a weakened immune system may develop severe pneumonia or other serious complications.
Your healthcare provider can test for the flu in several ways. This test usually gives results quickly. Immunofluorescence is another test and uses a staining technique. Results from these tests are not as accurate as viral cultures, yet another type of influenza test. But these tests are faster and easier and are commonly used for initial 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 influenza A or B virus. 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
Your healthcare provider may also order other tests, including an immunofluorescence antibody test, viral culture, or reverse transcriptase polymerase chain reaction. Testing for influenza antigens is considered a screening test. Your provider may use more accurate tests if he or she thinks 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 signs of the virus were found and that you don't have the flu. But 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.
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. Your healthcare provider may order more tests if he or she needs to confirm this.
This test requires a sample of mucus or other secretions from your nose or throat. Your doctor will use a sterile swab to collect the sample.
Another way of taking a sample requires a nasopharyngeal aspirate (NPA). In this procedure, a health care provider will inject saline solution into your nose and then collect the sample.
You may feel discomfort or gagging sensations 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.