Rheumatoid factor among post coronavirus disease 2019 cases: a preliminary report

To the Editor, Severe acute respiratory syndrome coronavirus 2 infection or coronavirus disease 2019 (COVID-19) is an important emerging disease. This viral infection is a respiratory tract infection that can cause fatality. The dysfunction of the immunological process of COVID-19 patient case is well mentioned, and there might be the formation of autoimmunity. Here, the authors report on rheumatoid factor test result after COVID-19. The data on 50 patients (25 males, 25 females; aged 29–70 years old) who have ever had a previous negative result of rheumatoid factor. The protocol of this retrospective study is approved by the local ethical committee (MAC 2021-18, approved April 8, 2021). All cases have negative rheumatoid factor result (titer < 10 IU/ml, normal range 0–18 IU/ml). Regarding the rheumatoid factor test in COVID-19, there are few reports. Cross-reactions between rheumatoid factor and Immunoglobulin M (IgM) severe acute respiratory syndrome coronavirus 2 is proposed [1]. Further researches are recommended. According to our best knowledge, this is one of the first world reports on rheumatoid factor among cases who have clear history of no previous positive rheumatoid factor after COVID-19 Acknowledgements Authors’ contributions: B.J. − 50% ideas, analysis, drafting, revising, and approval for final submission. V.W. − 50% ideas, analysis, drafting, revising, and approval for final submission. Conflicts of interest There are no conflicts of interest.