Diagnosis

Your doctor will conduct a physical exam, look for signs and symptoms of influenza, including H1N1 flu (swine flu), and possibly order a test that detects influenza viruses such as H1N1.

There are several tests used to diagnose influenza, but not everyone who has the flu needs to be tested. Your doctor may diagnose you with influenza based on your signs and symptoms. In most cases, knowing that someone has the flu doesn't change the treatment plan. Doctors are more likely to use a test to diagnose flu if:

• You're already in the hospital
• You're at high risk of complications from the flu
• You live with someone who is at greater risk of flu complications

Your doctor may also use a test to determine whether a flu virus is the cause of your symptoms, or if you have or are showing signs of another problem besides the flu, such as:

• Heart problems, such as heart failure or an infection of the heart muscle
• Lung and breathing problems, such as asthma or pneumonia
• Brain and nervous system problems, such as encephalopathy or encephalitis
• Septic shock or organ failure

In some cases, your doctor may suggest that you be tested for influenza. He or she may use various tests to diagnose influenza. Polymerase chain reaction (PCR) testing is becoming more common in many hospitals and labs. This test may be done while you're in your doctor's office or in the hospital. PCR testing is more sensitive than other tests and may be able to identify the influenza strain.

During the COVID-19 pandemic, it's possible to have a test to diagnose both influenza and COVID-19. It's possible to have both COVID-19 and influenza at the same time.