Key takeaways Flu tests are quick, taking only a minute to collect a sample with results ready in 15 to 30 minutes, though their accuracy varies. Rapid molecular assays more accurate over rapid influenza diagnostic tests (RIDTs) in detecting influenza. Flu tests can have false negative results, with RIDTs detecting the flu virus antigen between 50% to 70% of the time, but if positive, the likelihood of having influenza is high.