Clinical significance of serum IgM and IgG levels in COVID-19 patients in Hubei Province,China

Background:There have been many studies about coronavirus disease 2019(COVID-19),but the clinical signifi-cance of quantitative serum severe acute respiratory syndrome-coronavirus-2(SARS-CoV-2)-specific IgM and IgG levels of COVID-19 patients have not been exhaustively analyzed.We aimed to investigate the time profiles of these IgM/IgG levels in COVID-19 patients and their correlations with clinical features.Methods:A multicenter clinical study was conducted from February 20 to March 52020.It involved 179 COVID-19 patients(108 males and 71 females)from five hospitals in Huangshi in Hubei Province,China.To detect SARS-CoV-2-specific IgM/IgG,quantitative antibody assays(two-step indirect immunoassays with direct chemilu-minescence technology)based on the nucleocapsid protein(NP)and spike protein 1(S1)were used.For normally distributed data,means were compared using the t-test,𝜒2-test,or exact probability method.For categorical data,medians were compared using Mann-Whitney U test.Results:The median age was 57(44-69)years(58[38-69]for males and 57[49-68]for females).The median duration of positive nucleic acid test was 22.32(17.34-27.43)days.The mortality rate was relatively low(3/179,1.68%).Serum SARS-CoV-2-specific IgG was detected around week 1 after illness onset,gradually increased until peaking in weeks 4 and 5,and then declined.Serum IgM peaked in weeks 2 and 3,then gradually declined and returned to its normal range by week 7 in all patients.Notably,children had milder respiratory symptoms with lower SARS-CoV-2-specific IgM/IgG levels.The duration of positive nucleic acid test in the chronic obstructive pulmonary disease(COPD)group was 30.36(18.99-34.76)days,which was significantly longer than that in the non-COPD group(21.52[16.75-26.51]days;P=0.025).The peak serum SARS-CoV-2-specific IgG was sig-nificantly positively correlated with the duration of positive nucleic acid test.The incidence rate of severe and critical cases in the IgM hi group(using the median IgM level of 29.95 AU/mL as the cutofffor grouping)was about 38.0%(19/50),which was twice as much as that in the IgM lo group(18.4%;9/49).The patients with positive chest imaging and lymphocytopenia(<1×10^(9)/L)had a higher SARS-CoV-2-specific IgM level.Conclusions: Quantitative SARS-CoV-2-specific IgM and IgG levels are helpful for the diagnosis, severity classifi- cation, and management of COVID-19 patients, and they should be monitored in each stage of this disease.