Antibody Detection and Dynamic Characteristics in Patients with COVID-19

BACKGROUND: The corona virus disease 2019 (COVID-19) caused by the corona virus 2 (SARS-CoV-2) has been rapidly spreading nationwide and abroad. A serologic test to identify antibody dynamics and response to SARS-CoV-2 was developed. METHODS: The antibodies against SARS-CoV-2 were detected by an enzyme-linked immunosorbent assay (ELISA) based on the recombinant nucleocapsid protein of SARS-CoV-2 in patients with confirmed or suspected COVID-19 at 3-40 days after symptom onset. The gold standard for COVID-19 diagnosis was nucleic acid testing for SARS-CoV-2 by RT-PCR. The serodiagnostic power of the specific IgM and IgG antibodies against SARS-CoV-2 was investigated in terms of sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and consistency rate. RESULTS: The seroconversion of specific IgM and IgG antibodies were observed as early as the 4th day after symptom onset. In the confirmed patients with COVID-19, sensitivity, specificity, PPV, NPV, and consistency rate of IgM were 77.3% (51/66), 100%, 100%, 80.0%, and 88.1%, and those of IgG were 83.3.3% (55/66), 95.0%, 94.8%, 83.8%, and 88.9 %. In patients with suspected COVID-19, sensitivity, specificity, PPV, NPV, and consistency rate of IgM were 87.5% (21/24), 100%, 100%, 95.2%, and 96.4%, and those of IgG were 70.8% (17/24), 96.6%, 85.0%, 89.1%, and 88.1%. Both antibodies performed well in serodiagnosis for COVID-19 rely on great specificity. CONCLUSIONS: The antibodies against SARS-CoV-2 can be detected in the middle and later stage of the illness. Antibody detection may play an important role in the diagnosis of COVID-19 as complement approach for viral nucleid acid assays.