This study provides further evidence that serological testing is an effective diagnostic means for COVID, and showed that the positive rate and titer variance of IgG are higher than IgM.

Researchers retrospectively reviewed 43 patients with COVID-19 and 33 patients with suspected infection who were later excluded.  They measured the IgM/IgG titers by chemiluminescence immunoassay analysis.

The sensitivities of serum IgM and IgG antibodies were 48.1% and 88.9%, and the specificities were 100% and 90.9%, respectively. In COVID-19 group, IgM positive rate increased first then decreased over time, but IgG rate increased to 100% and was always higher than IgM. The median titer of IgG after patients were negative for the virus was twice what it was before.