Tests to Determine if You Have the Flu

Most influenza tests require a nasal swab to determine the type of influenza virus. Occasionally a blood sample is required for antibody testing. A variety of tests can determine the type of influenza virus in less than 30 minutes, though they are not as accurate as tests that take longer to obtain results.

Rapid Influenza Diagnostic Test (RIDT)

RIDT is a test that can quickly determine whether or not an infection is caused by the flu virus. A number of rapid tests are available, and they all require a simple nasal swab. The results are usually available on the same day. Rapid tests are most accurate when administered within the first 48 hours after symptoms appear. Some rapid tests can distinguish between flu virus types, but none of them can identify subtypes. The tradeoff for the speed of these tests is that they can miss up to 30 percent of flu infections.

Direct Fluorescent Antibody Stain

This test uses a nasal swab to determine the presence or absence of antibodies to the influenza virus in nasal secretions. The test can tell the difference between Type A and Type B virus, but it is unable to distinguish between virus subtypes of type A viruses like H1N1 or H3N2.

Influenza Virus Culture Test

The virus culture test is the most accurate test for influenza and can determine both virus type and subtype. A nasal swab is taken, and a culture of the virus is grown in a laboratory culture. Results can take three to 10 days, so a culture test is most often used by physicians to determine the dominant strain of virus circulating in a community or to find out whether unusual cases indicate a new strain is present.

Other Tests

If secondary infections like pneumonia or other complications are present, your physician may order other tests or procedures, including chest X-rays, sputum cultures, or blood tests.