Background: The outbreak of the novel 2019 coronavirus disease (COVID-19) was declared a global pandemic by the World Health Organization (WHO) on March 11, 2020 The diagnosis of COVID-19 is frequently based on a positive serological test We noted the occurrence of false-positive results for COVID-19 in the colloidal gold-based immunochromatographic strip (ICS) assay in sera from patients with autoimmune diseases (ADs) This study aimed to evaluate the possible reasons for the false-positive results in two ICS assays (Wondfo ICS and Innovita ICS) and to investigate the effect of urea dissociation in reducing false-positive results Methods: The sera of 135 patients with ADs, 13 confirmed COVID-19 patients, 95 disease controls, and 120 healthy controls were tested for immunoglobin M (IgM) and IgG against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) using Wondfo and Innovita ICS kits The distributions of auto-antibodies in antibody-positive and antibody-negative groups were also compared, and bivariable logistic regression was used to assess auto-antibodies associated with false-positive results A urea dissociation test of ICS was performed for the SARS-CoV-2 antibody-positive samples Results: Specificity of Wondfo ICS for the 95 disease controls was 94 74% compared to 98 95% and 96 84% for Innovita SARS-CoV-2 IgM and IgG, respectively Specificity of Wondfo ICS for the 120 healthy controls was 97 5% compared to 100% and 99 17% for Innovita SARS-CoV-2 IgM and IgG, respectively Specificity of Wondfo ICS for AD patients was 73 33% compared to 97 78% and 96 30% for Innovita SARS-CoV-2 IgM and IgG, respectively Sensitivity was 74 07% for Wondfo compared to 70 37% for Innovita IgM and 66 67% for Innovita IgG Using the Wondfo ICS, the percentage of elevated rheumatoid factor (RF) level (&gt;20 IU/mL) was higher in the SARS-CoV-2 antibody-positive group compared with the antibody-negative group [27/36 (75 0%) vs 34/99 (34 34%), P=0 001] The elevated RF was associated with antibody positivity, with an odds ratio of 4 671 [95% confidence interval (CI), 1 88-11 69] The specificity of the Wondfo ICS assay for the AD patients was increased from 73 33% to 94 07% after the urea dissociation assay Conclusions: An elevated serum RF level could lead to false-positive results when detecting SARS-CoV-2 antibodies using the Wondfo ICS kit, and the urea dissociation assay would be helpful in reducing the incidence of false-positive results
False-positive colloidal gold-based immunochromatographic strip assay reactions for antibodies to SARS-CoV-2 in patients with autoimmune diseases