Flu testing and diagnosis: How does it work?

Influenza (the flu) is a viral respiratory illness that affects millions of people each year. Symptoms can include fever, cough, stuffy or runny nose, sore throat, headache, chills and fatigue. A flu test is not always needed to diagnose the flu. However, in some cases, your healthcare provider may need to confirm if you have the flu, so they may recommend testing.

It’s common for healthcare providers to diagnose the flu based on symptoms and an exam, especially during flu season when the flu is going around your community. Sometimes a flu test may not be performed because guidelines recommend that you be treated anyway if you have flu symptoms and are at risk for serious illness or complications.

There are a number of tests used to diagnose the flu. The most common are rapid influenza diagnostic tests (RIDTs), and they may be performed in a healthcare provider’s office or at home. RIDTs work by detecting antigens (parts of the virus) that stimulate an immune response. A rapid molecular assay is another flu test that works by detecting genetic material of the virus. In addition to rapid tests, there are several more accurate and sensitive flu tests that must be performed in specialized laboratories, such as those found in hospitals or state public health laboratories.

A flu test typically involves a healthcare provider collecting a sample from the inside of your nose or back of your throat using a sterile swab. The swab is then tested for the flu. You can schedule a COVID-19 and flu combination test at Walgreens. Depending on your state, a Walgreens pharmacist may be able to prescribe antiviral treatment if you test positive for the flu. We also provide over-the-counter options to test for influenza, COVID-19, and other respiratory viruses.

Rapid flu tests including RIDTs and rapid molecular assays take about 10–30 minutes to get results, depending on the type of test used. Other types of tests that can only be completed in a clinical setting are sent to a lab for analysis and usually take longer to receive results.

Accuracy of the flu test depends on which kind of test is performed and the type of influenza that’s going around. While RIDTs are the most common flu tests, they are not as accurate as molecular assays. RIDTs are more accurate when performed during the first four days of symptoms. However, because younger children tend to shed the virus for longer, RIDTs may detect influenza for more than four days after symptom onset. In general, if you receive a positive rapid test during a flu outbreak, it likely means you’re infected with the flu. Note that false negative (meaning the test is negative but you really have the flu) and false positive (meaning the test is positive but you actually do not have the flu) test results can occur.

At-home rapid influenza tests can detect influenza viruses, while multi-virus (multiplex) respiratory test kits can detect multiple respiratory viruses at the same time, including influenza A and B, respiratory syncytial virus (RSV), and SARS-CoV-2, the virus that causes COVID-19. These over-the-counter tests can provide results in as little as 15 to 30 minutes and are available in stores and online. Some rapid tests can be used for children as young as 6 months old. However, for children younger than 13 years of age, an adult caregiver should perform the test. To help ensure accurate results, carefully follow all instructions included with the test kit. If you have questions about how to use the test or whether it is right for you or your child, talk with your healthcare provider before use.

Most people who have the flu have mild symptoms and recover without treatment. Still, the flu can be serious, and certain people are more likely to develop complications. This includes people 65 years and older, children 5 years and younger (especially those younger than 2 years), children with neurologic conditions, pregnant women and people with asthma, diabetes, cancer,  heart disease, stroke, human immunodeficiency virus (HIV) or acquired immunodeficiency syndrome (AIDS). If you have worrisome symptoms, aren’t getting better or are at risk for complications, contact your healthcare provider. They can decide if you need to be tested for the flu and recommend treatments.

Clinically reviewed and updated by Julie McDaniel, MSN, RN, CRNI July 2026.