Influenza Tests

These are tests ordered by your caregiver to determine if you likely have an infection caused by an influenza virus. Influenza is also called "the flu". Test results may help your caregiver make rapid treatment decisions. The test also helps them determine whether or not the flu has come to your community. Influenza testing relies on detecting a virus that is shed in the respiratory secretions of the person infected. Detectable flu virus is usually only shed for the first few days that a person is ill. Therefore, testing must be done during this early time period.

The sample to be tested depends on the testing method being used and the age of the patient. The methods used are usually a:

  • Nasopharyngeal (NP) swab.

  • Nasal aspirate.

  • Nasal wash.

  • Throat swab under approved circumstances.

The flu is a common respiratory illness that typically affects many people each winter season. There are two types of flu virus: A and B. Usually, a single strain of flu virus A will predominate during a particular flu season. However, there may be a mixture of A and B strains causing outbreaks in the community at the same time. The usual symptoms are:

  • Headache.

  • Exhaustion.

  • Fever.

  • Stuffy nose.

  • Chills.

  • Sore throat.

  • Muscle pains.

  • Cough.

Anti-viral medications have been developed to treat either flu A alone, or both A and B. These medications, if given within 48 hours of the onset of symptoms, can reduce the severity of symptoms. The medications can also reduce the time that a patient is sick by about a day and can be helpful in limiting infection spread to other family or household members. The medications will not help if given after 48 hours of the onset of symptoms. They also do not work against infections caused by other viruses or infections caused by any bacteria.

Rapid flu tests are available and have become the most frequently used test for flu.

  • Depending on the method, it may be completed in the caregiver's office in less than 30 minutes. It can also be sent to a lab, with the results available the same day.

  • Depending on the particular type of test used, it can identify flu A, a mixture of A and B, or differentiate between A and B.

  • Rapid flu testing can be used to help diagnose this infection, determine treatment options for a patient, and if negative can suggest that an alternative illness may be present. These are not perfect tests because up to 30% of flu infected persons will test negative. Test results will also occasionally be positive when the patient does not have a flu infection. Still, it is a quick way to determine whether someone is more likely than not to have flu.

Another test that your caregiver may order is a viral culture.

  • In this test, the flu virus is actually grown and identified in the lab.

  • It has the advantage of identifying which viruses (A, B, or even some other virus) and which strains of flu virus are present. It is useful for documenting that flu (A and/or B) has reached a community. It is also useful for identifying outbreaks in particular populations. These populations could be nursing homes, schools, or neighborhoods. Identifying these outbreaks can assist healthcare workers in the prevention and treatment of the flu throughout a community.

  • Its main disadvantage is that it takes one to several days to get a result. This is less than ideal for the caregiver who would like to prescribe treatment while the patient is still in the office.

Rapid flu tests are typically used within the first 48 hours of symptoms. This helps diagnose flu and determine if anti-viral medications may be of benefit. They can also be ordered within the first week to help identify outbreaks. Viral cultures are usually used to track flu outbreaks. They also identify the particular strain that is causing them. Sometimes an unexpected flu strain will show up. Viral cultures are also used to identify other viral infections that cause clinical symptoms similar to flu.


Your caregiver will go over your test results with you. They will also discuss the importance of this test. In general, a positive rapid flu test means you most likely have the flu. It does not tell your caregiver how severe your symptoms are likely to be or whether or not you may experience any secondary complications from this infection.

Positive flu cultures can give your caregiver additional information about the strain infecting you. This is often not in time to benefit your recovery. It is, however, useful information for your caregivers to share with other caregivers as they treat your family, friends, and neighbors, and to share with public health agencies in your community who help establish preventive interventions in your community.

Negative flu tests may mean that you have something other than the flu. It could also mean that there is not sufficient virus in the specimen to allow it to be detected.


  • Make sure you receive the test results. Ask as to how these results are to be obtained if you have not been informed. It is your responsibility to obtain your test results.

  • Your caregiver will provide further instructions or treatment options if necessary.