A doctor is usually able to diagnose
a case of influenza by simply observing common symptoms and noting the presence
of influenza in the local community. Most people will not require tests for
However, laboratory tests are sometimes
necessary for certain high-risk individuals, such as children younger than
five, adults over the age of 65, and pregnant women. These tests can help the
doctor determine the specific strain of flu present in an individual. They can
also help the doctor verify that the illness is not caused by another pathogen
that produces similar symptoms. Influenza’s symptoms are similar to other respiratory
infections including, but not limited to, parainfluenza viruses, respiratory
syncytial virus (RSV), and adenoviruses.
Laboratory tests may be helpful in
determining treatment options for the patient as well. They can also help the
doctor to establish whether influenza is the cause of an outbreak in a closed
setting such as a hospital, nursing home, or summer camp.
tests require a nasal or throat 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.
However, these tests are not as accurate as those that take longer to obtain
results. The following tests are those most commonly used in influenza testing.
Diagnostic Test (RIDT)
RIDT is a test that
can quickly determine whether a patient’s symptoms are caused by the flu virus
or by another viral or bacterial infection that requires more serious treatment.
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 A and B, but none of them can identify
subtypes. Additionally, the American Association for Clinical
Chemistry (AACC) notes that the tradeoff for the speed of these tests is
that they can miss up to 30 percent of flu infections.
Antibody Stain (DFA)
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. However, it is unable to distinguish between subtypes of Type A
viruses like H1N1 or H3N2.
The virus culture
test is the most accurate test for influenza and can determine both virus type
and subtype. For this test, a nasal swab is taken. Then, a culture of the virus
is grown in a laboratory. Results can take three to 10 days.
Sometimes a culture
test is taken to confirm a rapid flu test. It can also find other respiratory
viruses as well.
This type of
influenza test also helps healthcare workers determine the dominant strain of
virus circulating in a community or find out whether unusual cases indicate
that a new strain is present. Information from these culture tests is also used
to formulate the next year’s flu vaccine.
infections like pneumonia or other complications are suspected, your physician
may order other tests or procedures. These may include chest X-rays, blood
tests, or sputum cultures. A sputum culture is used to test substances from the
lungs and bronchi (the tubes that carry air to the lungs) to determine whether
an infection is present.