Part 11 of IVD Hall of Fame
« TDM Assays
Rapid influenza diagnostic tests are immunoassays that can detect the presence of influenza A and B viral nucleoproteins in respiratory specimens. Commonly immunochromatography is used to detect a reaction between monoclonal antibodies and the M or NP nucleoprotein of interest; a signal to indicate a reaction has occurred may be detected visually or by automated reader. Results can be generated in 15 to 30 minutes. A recent meta-analysis evaluating test performance indicates these tests have a modest sensitivity (mean of 62%s ranging from 4.4 to 100%) but a consistently high specificity (mean of 98% ranging from 51 to 100%).
In patients with signs and symptoms of influenza, rapid tests when positive help identify patients who should receive antiviral therapy (treatment is most effective if given within the first 48 hours after onset of disease). Because of the modest sensitivity noted above, negative tests cannot be used to rule out disease particularly during seasons when influenza activity is high. Testing is a prominent feature of diagnostic guidelines provided by CDC and other public health groups.
Before the introduction of rapid tests, physicians relied on old-fashioned clinical judgment to make a diagnosis or influenza. In patients with signs and symptoms of disease who are found to be rapid test negative, this is still the diagnostic method of choice. Studies in a variety of settings (emergency rooms, hospitalized patients) and in varying age groups (pediatrics, adults) suggest positive tests can be helpful in identifying patients who warrant immediate antiviral therapy. However, there is a paucity of studies documenting changes in outcomes. More work is in order to better understand how the landscape has changed since introduction of these tests.
There are more than a dozen FDA cleared tests able to detect both types of influenza in point of care settings. Some of these have been designated as suitable for use in waived laboratory settings (under CLIA).
There appears to be intense interest in improving performance for these assays to increase sensitivity and to eventually allow for discrimination of influenza subtypes. As a result there are intense ongoing efforts to reformulate and optimize all components of these rapid influenza systems including reagents, test strips, instruments when used, and collection instructions and materials. Point of care testing for influenza is a paradigm for how technology can be brought to the patient bedside in a manner that can lead to improved decision making for infectious disease.