Heat inactivation of serum interferes with the immunoanalysis of antibodies to SARS‐CoV‐2

BACKGROUND: The detection of serum antibodies to the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) is emerging as a new tool for the coronavirus disease 2019 (COVID‐19) diagnosis. Since many coronaviruses are sensitive to heat, heating inactivation of samples at 56°C prior to testing is considered a possible method to reduce the risk of transmission, but the effect of heating on the measurement of SARS‐CoV‐2 antibodies is still unclear. METHODS: By comparing the levels of SARS‐CoV‐2 antibodies before and after heat inactivation of serum at 56°C for 30 minutes using a quantitative fluorescence immunochromatographic assay RESULTS: We showed that heat inactivation significantly interferes with the levels of antibodies to SARS‐CoV‐2. The IgM levels of all the 34 serum samples (100%) from COVID‐19 patients decreased by an average level of 53.56%. The IgG levels were decreased in 22 of 34 samples (64.71%) by an average level of 49.54%. Similar changes can also be observed in the non–COVID‐19 disease group (n = 9). Of note, 44.12% of the detected IgM levels were dropped below the cutoff value after heating, suggesting heat inactivation can lead to false‐negative results of these samples. CONCLUSION: Our results indicate that heat inactivation of serum at 56°C for 30 minutes interferes with the immunoanalysis of antibodies to SARS‐CoV‐2. Heat inactivation prior to immunoanalysis is not recommended, and the possibility of false‐negative results should be considered if the sample was pre‐inactivated by heating.