If the Test Fits: Diagnosis to Aid in the Treatment of Influenza

Influenza is a significant cause of morbidity and mortality worldwide, presenting with lethal complications such as acute respiratory distress syndrome (ARDS). Multiple ways to diagnose influenza include rapid antigen tests, flu polymerase chain reaction (PCR), and respiratory viral panels or multiplex PCR. However, they have different sensitivities and specificities. We present a case of a 70-year-old female who was admitted to the ICU for ARDS and had a high pretest probability of influenza. She had an initial rapid flu antigen test that was negative and a negative flu PCR. However, she tested positive for influenza A (H1N1) with a respiratory viral panel. We as physicians should take into consideration the different sensitivities and specificities diagnostic tests have and consider retesting patients who have a negative test in the context of a high pretest probability. We should also remember to begin antiviral therapy early in a patient with high suspicion of influenza with a severe clinical presentation despite not having a confirmed diagnosis.