Preliminary study of serum 2019-nCoV IgM and IgG antibodies in the diagnosis of COVID-19

Objective To analyze the clinical value of serum 2019 New Coronavirus (2019-nCoV) immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies in the diagnosis of novel coronavirus pneumonia (NCP). Methods A total of 116 patients diagnosed with NCP in the First Affiliated Hospital of Hunan University of Chinese Medicine and the First Affiliated Hospital of Xiamen University were enrolled from January to February 2020 as the disease group. A total of 134 cases, including 84 non-NCP inpatients and 50 healthy individuals served as the control group. Serum samples from all subjects were collected. A fully-automated chemiluminescence immunoassay analyzer was used to detect the concentration of 2019-nCoV IgM and IgG antibodies in serum. The sensitivity and specificity of the 2019-nCoV IgM and IgG antibody single test and combined detection were compared using the χ2 test. χ2 test and Wilcoxon’s rank sum test were used to compare the positive rates and concentrations of IgM and IgG antibodies in NCP patients before and after their 2019-nCoV nucleic acid tests turning negative, respectively. The change trend of 2019-nCoV antibody concentration in the process of NCP patients was analyzed by Wilcoxon’s rank sum test. Results The sensitivity of 2019-nCoV IgG (90.5%, 105/116) was higher than that of 2019-nCoV IgM (75.9%, 88/116), the difference was statistically significant (χ2=8.91, P<0.05); The specificity of 2019-nCoV IgG (99.3%, 133/134) was higher than that of 2019-nCoV IgM (94.0%, 126/134), the difference was statistically significant (χ2=5.63, P<0.05). The sensitivity (89.7%, 87/97) of 2019-nCoV IgM combined with IgG was higher than that of 2019-nCoV IgM, the difference was statistically significant ( χ2=6.89, P<0.05). The specificity (100%, 125/125) of 2019-nCoV IgM combined with IgG was higher than that of 2019-nCoV IgM, the difference was statistically significant ( χ2=7.70, P<0.05). After 2019-nCoV nucleic acid test converted to negative, the positive rate (52.9%, 9/17) and concentration [13.0 (4.9, 24.7) AU/ml] of serum 2019-nCoV IgM antibody were significantly lower than those when the nucleic acid test was positive, positive rate (88.2%, 15/17) and concentration [29.5 (14.0, 61.3) AU/ml] , respectively (χ2=5.10, Z=-3.195, both P<0.05). In the course of NCP, patients' serum samples were collected from the first day of diagnosis to every three days, three times in total. The first 2019-nCoV IgM and IgG antibody concentrations [19.4 (12.4, 63.7) AU/ml, 105.8 (74.8, 126.1) AU/ml, respectively] were significantly higher than the second concentrations [15.8 (7.1, 40.3)AU/ml, 80.5 (66.7, 105.9) AU/ml], Z were -2.897, -3.179, both P<0.05. Conclusions 2019-nCoV IgG antibody has a good application value in the diagnosis of NCP; The concentration of 2019-nCoV IgM antibody has a certain correlation with the detection of 2019-nCoV nucleic acid; The combination of 2019-nCoV IgM and IgG antibodies with 2019-nCoV nucleic acid test may be the best laboratory index for the diagnosis of NCP at present. Key words: Coronavirus; Pneumonia, viral; Immunoglobulin M; Immunoglobulin G; Nucleic acids; Sensitivity and specificity; Real-time polymerase chain reaction