Influenza (flu) tests

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At a Glance

Why Get Tested?

To identify the type or strain of flu virus that you have

When to Get Tested?

If your doctor wants to determine whether your flu-like symptoms are due to a particular type or strain of the influenza virus, or due to other causes

Sample Required?

Usually a nose or throat swab

The Test Sample

What is being tested?

Influenza (the flu) is a viral infection that tends to be seasonal, beginning in late July and disappearing in early spring. It is a common respiratory (affecting the lungs) illness that causes headaches, fever, chills, muscle pains, exhaustion, a stuffy nose, sore throat, and a cough. Symptoms of flu tend to be more severe and longer lasting than the flu-like symptoms caused by the common cold. Flu and its complications can lead to hospitalisations even death, especially in the very young, the elderly, and in those with lowered immune responses or pre-existing lung disease.

There are three types of influenza, known as A, B and C, each of which can change many times to create multiple strains. Influenza virus A is the most common and causes the most severe symptoms. Type B is less common and causes less severe symptoms, whilst type C usually causes only a mild illness (similar to the cold).

Flu testing relies on detecting virus that is being shed in the respiratory secretions of the person infected. Detectable virus is usually only shed for the first few days that a person is ill, so most testing must be done during this time period. Anti-viral medications have been developed to treat either influenza 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 and reduce the time that a patient is sick by about a day. (They will not help if given later and they will not work against other viruses or against bacterial infections).

These medications will only be prescribed if the person is at particular risk of complications and it is known that influenza A or B are circulating in the community. For otherwise healthy people, the treatment is to stay in bed and rest, drinking plenty of fluids, until the symptoms have cleared up.

In the flu test, DNA from the influenza virus is detected using a special technique known as PCR (Polymerase Chain Reaction). In addition, the influenza virus is actually grown and identified in the laboratory. The test can identify which viruses (A, B, or some other virus) and which strains of virus are present. It is useful for documenting that the flu (A and/or B) has reached a community, and for identifying outbreaks in particular populations, such as a nursing home, school, or neighbourhood. Identifying these outbreaks can assist healthcare workers in the prevention and treatment of the flu throughout a community and in the manufacture of the annual influenza vaccine.

How is the sample collected for testing?

A nasal swab is collected by having you tip your head back, then a swab (like a long cotton bud) is gently inserted into one of your nostrils until resistance is met (about 1 to 2 inches in), then rotated several times and withdrawn. This is not painful, but it may tickle a bit and cause your eyes to well-up. Sometimes a doctor may use a throat swab.

The Test

Common Questions

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.