Flu (Influenza) Test
Reviewed
A flu (influenza) test checks a sample of fluid from your nose or throat to find out if you are infected with a flu virus. It is a laboratory test that can be done as a rapid antigen test (RIDT) or a molecular test (PCR). The test detects seasonal influenza A and B viruses. Some tests also check for other respiratory viruses like COVID-19 or RSV. Results help guide treatment and infection control decisions.
Preparation and collection
No special preparation for most collection methods. For a sputum culture, you may be asked to drink extra water the night before and possibly avoid eating for 1-2 hours before the test. For bronchoscopy or BAL, you may need to fast for up to 12 hours and stop certain medicines. Follow your provider's instructions.
Understanding this test
Use the reference interval and units printed by the laboratory that performed the test. A result outside that interval is not a diagnosis by itself, and a result inside it does not rule out every condition. Your symptoms, history, medicines, timing, and related tests can change what the result means.
- False negatives are possible, especially with rapid antigen tests or if the sample is collected when the virus level is low.
- False positives are very uncommon but can occur.
What to do next
If you have a high risk of serious illness, contact your healthcare provider at the first sign of symptoms. Antiviral medicine works best when started within 2 days of symptoms. To lower your risk of getting the flu, wash hands often, avoid close contact with sick people, and get a yearly flu vaccine.