False‐positive semiquantitative immunochromatography assays for procalcitonin in three patients with rheumatoid arthritis—A case series

We report three rheumatoid arthritis (RA) patients with false‐positive procalcitonin (PCT) based on semiquantitative immunochromatography assays without infection, but who had negative PCT assay results based on quantitative methods. Immunochromatography was useful for screening; however, other heterophilic antibodies rather than rheumatoid factor were possible to affect, especially in RA flare.