Diagnosis
Flu is usually diagnosed by the symptoms, but often doctors will also take a rapid influenza test or other laboratory tests to support a diagnosis of flu.
Physical Exam
When you go to a hospital, they will do a medical exam to see if the cold or the flu is what you’re experiencing.
Physicians are likely to ask questions about the signs and symptoms (e.g., when they turn up, how serious they are, etc.), any underlying medical conditions, the history of vaccines (if you had a flu vaccine this season), as well as any vital signs such as the temperature, respiratory rate or heart rate. They listen to your lungs and test your breathing patterns to check for possible lung complications such as pneumonia.
Labs and Tests
Physical examinations are the mainstay of diagnosing colds and flu, but doctors also validate the diagnosis by using certain tools, such as laboratory tests. Although not everyone with flu-like symptoms needs to get labs performed, these tests can be especially helpful when determining which medication to prescribe or respond to an outbreak in a school or hospital.
Laboratory tests used to diagnose flu include quick diagnostic tests, serological testing, viral assays, and viral cultures.