Researchers from the Centers for Disease Control and Prevention found that while rapid influenza diagnostic test could accurately detect the virus in high concentrations, reverse real-time PCR testing should be done if a definitive determination is needed.
"We had gotten an increasing number of inquiries from physicians wanting to know if the rapid test would work at all on this novel strain, and, of course, off-shot of that is wondering what the sensitivity and specificity would be," says Michael Shaw, associate director for laboratory science in the CDC's influenza division.
The rapid tests, which are enzyme-based, were evaluated on 65 samples, 45 of which contained the novel H1N1 virus, five with seasonal H1N1, and 15 with seasonal H3N2, as determined by the CDC's rRT-PCR assay. The sensitivity of the tests was determined from their accuracy in calling samples with different viral titers, as based on the specimens' cycle threshold value. "They were more likely to yield a valid result if there was more virus there [and] that depends of course on how soon after symptom onset the sample was taken," he adds.
Shaw points out the study was limited to the common rapid tests and not controlled for how the samples were collected and transported.
Still, the rapid tests, when positive, are accurate. Negative results, however, aren't necessarily actually negative. In that case, clinicians should base their treatment on what is circulating in the area and, if a more concrete result is needed, rely on the rRT-PCR assay.