A Method To Prevent SARS-CoV-2 IgM False Positives in Gold Immunochromatography and Enzyme-Linked Immunosorbent Assays

J Clin Microbiol. 2020 May 26;58(6):e00375-20. doi: 10.1128/JCM.00375-20. Print 2020 May 26.


We set out to investigate the interference factors that led to false-positive novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) IgM detection results using gold immunochromatography assay (GICA) and enzyme-linked immunosorbent assay (ELISA) and the corresponding solutions. GICA and ELISA were used to detect SARS-CoV-2 IgM in 86 serum samples, including 5 influenza A virus (Flu A) IgM-positive sera, 5 influenza B virus (Flu B) IgM-positive sera, 5 Mycoplasma pneumoniae IgM-positive sera, 5 Legionella pneumophila IgM-positive sera, 6 sera of HIV infection patients, 36 rheumatoid factor IgM (RF-IgM)-positive sera, 5 sera from hypertensive patients, 5 sera from diabetes mellitus patients, and 14 sera from novel coronavirus infection disease 19 (COVID-19) patients. The interference factors causing false-positive reactivity with the two methods were analyzed, and the urea dissociation test was employed to dissociate the SARS-CoV-2 IgM-positive serum using the best dissociation concentration. The two methods detected positive SARS-CoV-2 IgM in 22 mid-to-high-level-RF-IgM-positive sera and 14 sera from COVID-19 patients; the other 50 sera were negative. At a urea dissociation concentration of 6 mol/liter, SARS-CoV-2 IgM results were positive in 1 mid-to-high-level-RF-IgM-positive serum and in 14 COVID-19 patient sera detected using GICA. At a urea dissociation concentration of 4 mol/liter and with affinity index (AI) levels lower than 0.371 set to negative, SARS-CoV-2 IgM results were positive in 3 mid-to-high-level-RF-IgM-positive sera and in 14 COVID-19 patient sera detected using ELISA. The presence of RF-IgM at mid-to-high levels could lead to false-positive reactivity of SARS-CoV-2 IgM detected using GICA and ELISA, and urea dissociation tests would be helpful in reducing SARS-CoV-2 IgM false-positive results.

Keywords: enzyme-linked immunosorbent assay; false-positive; gold immunochromatography assay; novel coronavirus; urea.

MeSH terms

  • Betacoronavirus / immunology*
  • COVID-19
  • COVID-19 Testing
  • Chromatography, Affinity / methods*
  • Clinical Laboratory Techniques / methods*
  • Coronavirus Infections / diagnosis*
  • Enzyme-Linked Immunosorbent Assay / methods*
  • False Positive Reactions
  • Humans
  • Immunoglobulin M / blood*
  • Pandemics
  • Pneumonia, Viral / diagnosis*
  • SARS-CoV-2


  • Immunoglobulin M