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.