Flu testing and diagnosis: How does it work?

By Jenilee Matz, MPH Jun 30, 2022 • 3 min

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.

How is the flu diagnosed?

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. Oftentimes, a flu test isn’t performed because if there is a high level of flu in the community and you have symptoms but test negative, guidelines recommend that you be treated anyway. 

How to test for flu

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. 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.

How long does a flu test take?

Flu tests performed in a healthcare provider’s office or clinic take about 10–30 minutes to get results, depending on the type of test used. Tests sent to a lab for analysis take longer to receive results.

How accurate is the flu test?

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, and they seem to be better at detecting the flu in children than adults. 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.

Are there at-home flu tests?

At-home rapid flu test screening kits and combination test kits that can identify infection with influenza A and B, respiratory syncytial virus, commonly known as RSV, along with SARS-CoV-2, the virus that causes COVID-19, are available. These tests involve collecting a sample at home, mailing that sample to the lab to be analyzed, and then receiving your results. However, at this time, these tests have not been approved by the U.S. Food and Drug Administration (FDA) and may not be available in all states.

What to do if you think you have the flu

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 June 2022.

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