False-positive detection of IgM anti-severe acute respiratory syndrome coronavirus 2 antibodies in patients with rheumatoid arthritis: Possible effects of IgM or IgG rheumatoid factors on immunochromatographic assay results

• Published in: SAGE open medicine 2022-03, Vol.10, p.20503121221088090-20503121221088090
• Main Authors: Oka, Shomi, Higuchi, Takashi, Furukawa, Hiroshi, Shimada, Kota, Hashimoto, Atsushi, Matsui, Toshihiro, Tohma, Shigeto
• Format: Article
• Language: English
• Subjects: Antibodies; Coronaviruses; Immunoassay; Original; Rheumatoid arthritis; Severe acute respiratory syndrome; Severe acute respiratory syndrome coronavirus 2; Smoke inhalation
• ISSN: 2050-3121; 2050-3121
• DOI: 10.1177/20503121221088090

Objectives: The severe acute respiratory syndrome coronavirus 2 causes coronavirus disease 2019. A serological test is conducted to determine prior infection by severe acute respiratory syndrome coronavirus 2. We investigated whether the results of anti-severe acute respiratory syndrome coronavirus 2 antibody tests are modified in patients with rheumatoid arthritis. Methods: Patients in Japan with rheumatoid arthritis were recruited at Sagamihara Hospital from July 2014 to October 2015 (n = 38; 2014 cohort) and at Tokyo Hospital from June to October 2020 (n = 93; 2020 cohort). Anti-severe acute respiratory syndrome coronavirus 2 antibodies were measured by electrochemiluminescence immunoassay or immunochromatographic assay. Results: Anti-severe acute respiratory syndrome coronavirus 2 antibodies were not detected in any of the samples from rheumatoid arthritis patients tested by electrochemiluminescence immunoassay. Anti-severe acute respiratory syndrome coronavirus 2 antibodies were detected by immunochromatographic assay in the 3 (7.9%) serum samples in the 2014 cohort and 15 (16.1%) serum samples in the 2020 cohort. The IgM rheumatoid factor levels were increased in rheumatoid arthritis patients with IgM anti-severe acute respiratory syndrome coronavirus 2 antibodies detected by immunochromatographic assay (mean ± standard deviation (IU/ml), 1223.0 ± 1308.7 versus 503.6 ± 1947.2; P = 0.0101). The levels of IgG rheumatoid factor were also upregulated in rheumatoid arthritis patients with IgM anti-severe acute respiratory syndrome coronavirus 2 antibodies detected by immunochromatographic assay (4.0 ± 0.7 versus 2.4 ± 0.9; P = 0.0013). Conclusion: The results of IgM anti-severe acute respiratory syndrome coronavirus 2 antibody testing by immunochromatographic assay are modified by IgM or IgG rheumatoid factors in rheumatoid arthritis patients.