CDC issues guidance on rapid influenza tests

Rapid influenza tests can be useful in diagnosis and treatment, but they often yield false-negative results, the CDC recently cautioned.

In a guidance statement released in December, the CDC outlined the appropriate use of rapid influenza tests for the 2010-2011 influenza season. The tests are easy to use and yield results in 15 minutes or less, making them helpful for confirmation of outbreaks, especially in institutional settings. However, they have limited sensitivity and predictive value, the agency said. Because of the high risk for false-negative results, a patient who tests negative but has signs and symptoms of flu should not be excluded from antiviral treatment. Testing is not always necessary in all patients, especially in a community known to already be affected by influenza. The CDC listed the following factors as potential influences on rapid-test accuracy:clinical signs and symptoms of influenza,prevalence of influenza in the population tested,time from illness onset to collection of respiratory specimens for testing,type of respiratory specimen tested, andaccuracy of the test compared to a reference test, such as reverse transcriptase polymerase chain reaction or viral culture.

To minimize false results, the CDC recommends that clinicians collect specimens as early as possible after illness onset (ideally within four days), follow manufacturer's instructions on acceptable specimens and appropriate handling, and confirm negative results with a reference test if a laboratory-confirmed diagnosis is needed.

The full guidance statement, which includes additional information on test interpretation and clinical algorithms to assist in decision making, is available online.