False-negative rates are high with the rapid influenza antigen test (RIAT) and can dangerously delay antiviral treatment for severely ill influenza patients, the authors of a new study warned.

In fact, a presentation at ASM Microbe, the American Society for Microbiology's annual meeting held recently in Atlanta, showed that RIAT results were false-negative in half of influenza cases in ICU patients.

Taiwanese researchers came to that conclusion after conducting a retrospective analysis of 307 patients with confirmed influenza requiring ICU admission at Chang-Gung Memorial Hospital, a tertiary medical center in Taiwan, from August 2009 to July 2017. RIAT was performed on 259 of the patients, 49% of whom tested negative.

The study team noted that, among the 307 cases, 45 either tested negative on all upper respiratory tract (URT) samples or did not have URT samples tested, meaning that the confirmed diagnosis in those cases relied on results from lower respiratory tract (LRT) samples.

Researchers noted that the point-of-care testing is valuable because a positive test result with high specificity confirms the diagnosis of influenza. On the other hand, according to the researchers, a negative test result and low sensitivity can mislead physicians to exclude an influenza diagnosis.

“Negative RIAT impedes physicians from dispensing antiviral medication. The clinical outcome of RIAT-negative critically ill severe influenza was at least equally grave with, if not worse than, those with positive RIAT,” the researchers concluded.