Are Rapid Influenza Antigen Tests Still Clinically Useful in Today's Molecular Diagnostics World?

Influenza virus infection and disease historically contribute to widespread cases of seasonal morbidity and in some cases mortality. Prompt and accurate diagnosis is crucial for optimal patient management. Rapid influenza direct antigen testing (RIDT) offers a faster turn-around-time for results but test performance (ie, sensitivity and specificity) varies widely. Nucleic acid amplification testing (NAAT) can offer a viable alternative. The objective of this retrospective study was to compare the test performance of RIDT with NAAT. RIDT testing included the Directigen EZ Flu A+B or the Veritor System for Rapid Detection of Flu A+B. NAAT employed the SimplexaTM Flu A/B™ RSV assay. A total of 5,795 specimens collected from October to March for the 2012/2013 (n=953), 2013/2014 (n=2060) and 2014/2015 (n=2783) seasons were co-tested by RIDT and NAAT. Using NAAT as the gold standard, RIDT tests had a sensitivity range of 0 to 15.7% and a specificity of 98.2 to 100% for influenza type A. For influenza type B, RIDT tests had a sensitivity of 0 to 33.3% and a specificity of 98.9 to 100%. These findings suggest that RIDT has unacceptably low sensitivity for both influenza A and influenza B, despite high specificity. The key advantage of RIDT in previous years (faster turnaround time) has been challenged by newer NAAT technology that provides results in a turn-around-time comparable to RIDT, but with superior test performance.