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

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

Qiang Wang #  1   2   3 , Qin Du #  1   3 , Bin Guo  1   2   3 , Daiyong Mu  4 , Xiaolan Lu  1   3 , Qiang Ma  1   2   3 , Yangliu Guo  1   2   3 , Li Fang  1   2   3 , Bing Zhang  4 , Guoyuan Zhang  5   3 , Xiaolan Guo  5   2   3
Affiliations

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

Qiang Wang et al. J Clin Microbiol. .

Abstract

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.

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Figures

FIG 1
FIG 1
SARS-CoV-2 IgM detected using GICA before and after urea dissociation. N1 and N2, SARS-CoV-2 IgM in serum of SARS-CoV-2 infection patients before and after urea dissociation test in GICA; N3 and N4, SARS-CoV-2 IgM in serum with RF-IgM-positive results before and after urea dissociation test in GICA.
FIG 2
FIG 2
AI of SARS-CoV-2 IgM detected using different urea dissociation concentrations of ELISA. When the dissociation concentration of urea was 4 mol/liter and the AI calculation method value was set to 0.371, the results determined for SARS-CoV-2 IgM in 19 sera with RF-IgM positivity turned negative, whereas the results determined for SARS-CoV-2 IgM in the 14 sera from COVID-19 patients remained positive.
See this image and copyright information in PMC

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