Antibody Detection and Dynamic Characteristics in Patients with COVID-19

Abstract

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 4^th 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.