How is Flu Diagnosed?

What is the flu and why is diagnosis important?

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 and treat 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 do doctors diagnose the flu?

 If you think you have flu symptoms, your provider may evaluate you in person or through a virtual (telehealth) visit. They'll ask about your symptoms, review your medical history and may perform a physical exam. In some cases, they’ll order a flu test to confirm the diagnosis and guide treatment.

Do I need to see a doctor in person for a flu diagnosis?

You can get a flu diagnosis through an in-person or virtual appointment. Virtual visits allow you to get care from the comfort of home, but in-person care may be better for people at higher risk of complications—such as children under 5, adults over 65, pregnant individuals, and people with chronic health conditions.

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.

When should you get tested for the flu?

Flu testing is recommended if you have symptoms like fever, sore throat, cough or body aches—especially within the first 48 hours of symptoms. Early testing helps guide treatment and may reduce the risk of complications.

Testing may also be done to help public health officials track flu outbreaks in your area.

What are the different types of flu tests?

All flu tests use a swab from your nose or throat. Common types include:

• Rapid influenza diagnostic tests (RIDTs): Performed in a provider’s office with results in 10–15 minutes, but less accurate.
• Rapid molecular assays: More accurate, with results in 15–20 minutes.
• RT-PCR and viral culture tests: Sent to a lab, with results in several hours or a few days.

Can I use an at-home flu test kit?

Yes. At-home flu tests (some combined with COVID-19 and RSV testing) use a nasal swab and provide results in about 30 minutes. These tests are convenient, but you must follow instructions carefully to ensure accuracy. They may not be the best option for people at high risk of severe illness.

How accurate are flu tests?

Flu test accuracy depends on the type of test and the circulating flu strain:

• RITDs are 50% to 80% accurate, meaning false negatives are possible.
• Molecular assays are more reliable, with 90% to 95% accuracy.

Your provider may recommend a follow-up test or begin treatment based on your symptoms if the test result is unclear.

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

If you test positive, your provider may recommend:

• Rest and staying home
• Antiviral medication to reduce severity and recovery time
• Getting the flu vaccine 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.

Why is early flu diagnosis important?

Early diagnosis helps you feel better faster, reduces the risk of serious complications and prevents spreading the flu to others.

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.