How is Flu Diagnosed?

Influenza (the flu) is a contagious respiratory (breathing) illness caused by the influenza virus. A timely and accurate diagnosis is important for effective treatment and stopping the spread of the virus. 

At Banner Health, we want you to get the best care so that you can return to good health as fast and safely as possible. Part of that care is learning how the flu is diagnosed.

Who can diagnose the flu?

Several health care providers can diagnose and treat the flu, including:

• Primary care physicians: Your family or general doctor
• Nurse practitioners and physician assistants: Specialists who assist doctors
• Pediatricians: Doctors who specialize in children’s health care
• After-hours or urgent care specialists: Easy-to-access medical professionals at clinics around town
• Hospitalists and emergency department physicians: Doctors in hospital settings, for people at high-risk and/or those with severe cases of the flu

How is the flu diagnosed?

If you think you have flu symptoms, taking the right steps for proper medical care is essential. You can visit your health care provider in person or virtually (online) using a telehealth appointment.

Virtual visits allow you to get the care you need from the comfort of your home. However, this option may not be best if you need more hands-on care. This includes people at high risk for complications, such as children under 5 years old, adults over 65, pregnant people and people with chronic medical conditions and/or weakened immune systems.

Your provider may use the following methods to diagnose the flu:

• Medical history and physical exam: Your provider will ask you about your symptoms, medical history and any recent exposure to the flu virus. They will also give you a physical exam to rule out other illnesses.
• Flu testing (testing for influenza): In some instances, your provider may request a test to figure out which type of flu virus you have.

Who should get tested for the flu?

Your provider may recommend a flu test if you show symptoms such as a high fever, sore throat, coughing or body aches. They may also order a flu test if you are at greater risk for complications.

Getting a quick flu diagnosis can help you with treatment, including the use of antiviral medications. Ideally, testing should occur within the first 48 hours (about two days) of experiencing symptoms.

You may also need to take a flu test so that public health officials can determine if there is an outbreak of the flu in your community.

What are the different kinds of flu tests?

There are several tests used to diagnose the flu. All involve a quick swab of your nose or throat to get a viral sample. The most common are rapid influenza diagnostic tests (RIDTs). Other tests include rapid molecular assays and specialty flu tests, including the reverse transcription-polymerase chain reaction (RT-PCR) test.

• RIDT is a quick test done in your provider’s office. While the test provides quick results (usually in 10 to 15 minutes), it may not be as accurate as other flu tests. You may still have the flu, even if your rapid test result is negative.
• Rapid molecular assays are more sensitive and accurate tests and are often used during flu outbreaks or if an RIDT’s results are in doubt. These tests give results in about 15 to 20 minutes.
• Other lab tests include RT-PCR and viral culture tests. These tests are sent to a laboratory. You can expect results within several hours or a few days.

At-home rapid flu screening kits and combination test kits that identify RSV (respiratory syncytial virus), flu and COVID-19 are also now available. These tests involve collecting your own sample using a nasal swab. Results are available in about 30 minutes—no lab required. 

These kits can save you time and an office visit, but you must carefully follow test directions to get accurate results.

How accurate is the flu test?

The accuracy of the flu test depends on the type of test and the flu strain that is going around.

RIDTs are the most common flu test, but molecular assays are more sensitive and accurate. RIDTs detect the presence of the flu virus 50% to 80% of the time, so false negative results are possible. Molecular assays, however, are 90% to 95% accurate.

What should I do if I test positive for the flu?

Your provider will provide treatment options if you test positive for the flu. This may include rest and self-care, taking antiviral medication and getting a flu shot once you recover (if you haven’t had one this season).

The results from your test will likely be anonymously shared with your state’s Department of Health to help the Centers for Disease Control and Prevention (CDC) track any flu outbreaks.

Learn more about treating the flu.

The importance of early diagnosis and prevention

Getting diagnosed with the flu is important for your well-being and the well-being of those around you. Early diagnosis allows for quick treatment, lessens any complications and helps limit the spread of the virus.

Remember, prevention is always better than getting sick. Getting the flu vaccine every year and regular hand washing is your best defense against the flu.