Correlation of the ratio of IgM/IgG concentration to days after symptom onset (IgM/T or IgG/T) with disease severity and outcome in non-critical COVID-19 patients

BACKGROUND: Correlation of SARS-CoV-2 serum antibodies with COVID-19 development and outcome has not been fully studied Due to the time dynamic of antibodies, the antibody concentration of the same patient varies greatly at different times during the course of the disease Therefore, our study used IgM/T or IgG/T (the ratio of serum antibody concentration to days after symptom onset) to reflect the patient's humoral immune status, and analyzed their correlation with COVID-19 development and outcome METHODS: Clinical data of 50 non-critical COVID-19 patients were retrospectively analyzed Time-resolved fluorescence immunochromatography was used to quantitatively detect SARS-CoV-2 IgM and IgG Correlation analysis was performed RESULTS: IgM antibody was positive on day 5 of symptom onset, increased within 2 weeks, and then gradually decreased However, IgG antibody was positive on week 2 of symptom onset and continued to increase since Additionally, IgM/T, but not IgG/T of recovery period (Spearman rho=0 17;P=0 283), was negatively correlated with disease course in 2 weeks of symptom onset (Spearman rho=-0 860;P=0 000) IgG/T of recovery period was positively correlated with clinical classification (Spearman rho=0 432;P=0 004), number of involved lung lobes (Spearman rho=0 343;P=0 026), and lung lesions (Spearman rho=0 472;P=0 002) CONCLUSIONS: Within 2 weeks of symptom onset, higher IgM/T indicates faster recovery and shorter disease course In recovery period, higher IgG/T suggests more serious disease IgM/T or IgG/T may predict disease severity and outcome in non-critical COVID-19 patients