Clinical significance of the serum IgM and IgG to SARS‐CoV‐2 in coronavirus disease‐2019

Objective To explore the clinical value of serum IgM and IgG to SARS‐CoV‐2 in COVID‐19. Methods 105 COVID‐19 patients were enrolled as the disease group. 197 non‐COVID‐19 patients served as the control group. Magnetic chemiluminescent immunoassay (MCLIA) was used to detect the IgM and IgG. Results The peak of positive rates of SARS‐CoV‐2 IgM was about 1 week earlier than that of IgG. It reached to peak within 15–21 days and then began a slowly decline. The positive rates of IgG were increased with the disease course and reached the peak between 22 and 39 days. The differences in sensitivity of the three detection modes (IgM, IgG, and IgM + IgG) were statistically significant. The largest group of test cases (illness onset 15–21 days) showed that the positive rate of IgG was higher than IgM. Also, the sensitivity of IgM combined with IgG was higher than IgM or IgG. IgM and IgG were monitored dynamically for 16 patients with COVID‐19, the results showed that serological transformation of IgM was carried out simultaneously with IgG in seven patients, which was earlier than IgG in four patients and later than IgG in five patients. Conclusion The detection of SARS‐CoV‐2 IgM and IgG is very important to determine the course of COVID‐19. Nucleic acid detection combined with serum antibody of SARS‐CoV‐2 may be the best laboratory indicator for the diagnosis of SARS‐CoV‐2 infection and the phrase and predication for prognosis of COVID‐19.
Antibody response to SARS‐CoV‐2 in 105 COVID‐19 patients. (A) The positive rate of SARS‐CoV‐2 antibody in 105 patients. (B) The changes of antibody titers to SARS‐CoV‐2 in 105 patients.