2020 Volume 69 Issue 3 Pages 463-467
An influenza virus rapid antigen detection test (RADT) based on the immunochromatography technique is prevalently used as the point-of-care testing (POCT) in many clinical settings. It is well known that this RADT kit sometimes shows false-negative results. On the other hand, a false-positive result also occasionally occurs. We encountered the case of a patient whose clinical nasal swab specimen was positive for both A and B influenza antigens as determined with the RADT kit used for rapid influenza diagnosis. However, the patient was found not to have influenza virus infection because the specimens were confirmed to be negative by virus isolation and genetic detection by PCR. Moreover, the RS virus was isolated from the specimens. Thus, we considered it as a case with a false-positive reaction occurring in the RADT kit. We considered the double-positive and false-positive cases as very interesting and explored the reasons for such cases. We hypothesized as follows: there was/were some material(s) other than the antigen in the specimen and it/they reacted with the mouse anti-influenza antigen monoclonal antibody used in the RADT kit, and it/they acts/act as if it/they was/were the influenza antigen exhibiting the two reaction lines that appeared at the A and B sites on the immunochromatography sheet of the kit. To prove it, the RADT kit was used again after the pretreatment of the specimen with an excess amount of the purified mouse IgG for the IgG to competitively react with the antibody on the reaction lines. As a result, the reaction became negative. These findings strongly suggest that the false-positive result was caused by the reaction of some material in the specimen with the mouse antibody used in the RADT kit.
