Exams and Tests

There is no way to tell what type of influenza a person has without doing tests. In most cases, the diagnosis of flu is determined by the symptoms, especially when these occur during the peak flu season (late fall and winter in the U.S.). Sometimes, the doctor may need to perform special tests to be sure the seasonal influenza virus is responsible for the symptoms.

To identify whether the virus is present and to test for the type of influenza, a sample is taken from the back of the throat and/or nose. The doctor uses a cotton-tipped wooden stick and simply rubs the cotton tip at the back of the throat and/or inside the nose. Alternatively, samples may be obtained by rinsing saltwater (saline) solution through the nose and throat and aspirating the fluid back into a specimen jar. The sample is sealed in a packet and sent to the lab for testing. Some offices may use a rapid test that can be done in the office with the result available in 30 minutes. Some rapid tests detect only influenza A virus, while others can detect both influenza A and influenza B. Some cases of flu may be missed by the rapid tests.

Importantly, routine diagnostic tests available in the doctor's office probably cannot determine whether a case of the flu is due to bird flu or human flu. If bird flu is suspected, the samples would be sent to a reference laboratory (usually through the health department) for special testing. If a patient is in the hospital, the physician may recommend a bronchoscopy, which involves slipping a tube through the mouth into the lungs to aspirate secretions.