Impact of heat-inactivation on the detection of SARS-CoV-2 IgM and IgG antibody by ELISA.

BACKGROUND:To establish a safe and accurate method for detecting SARS-CoV-2 IgM and IgG, we assessed the impact of sera after heat-inactivation on the SARS-CoV-2 IgM and IgG levels measured by ELISA-immunoassay. METHODS:The serum samples of 62 patients with COVID-19 and 18 healthy controls were collected in Hankou's Hospital of Wuhan from February 27 to March 6, 2020. Before and after the samples were inactivated, the levels of IgM and IgG antibodies were measured. RESULTS:The indexes of antibodies after inactivated were significantly higher than those in fresh sera, while the positive rates in all participants or in patients with COVID-19 did not change. The positive coincidence rate, negative coincidence rate and total coincidence rate of IgM antibodies before and after inactivation were 100.00% (55/55), 96.00% (24/25) and 98.75% (79/80), respectively (κ = 0.971, P < 0.001), while those for IgG antibodies were 98.21% (55/56), 91.67% (22/24) and 98.75% (79/80) respectively (κ = 0.910, P < 0.001). These results showed a good consistency. CONCLUSIONS:Heating-activation does not decrease the diagnostic efficacy of SARS-CoV-2 IgM or IgG antibodies. Sera inactivated by heating at 56 °C for 30 min should be recommended to minimize the risk of virus contamination of laboratory staff.