In this issue of Clinical Infections Diseases, F Xiang et al present a serologic study of 85 nucleic acid test (NAT) SARS-CoV-2 positive patients and 24 NAT negative patients who had symptoms suspicious for COVID-191. Sixty controls were also evaluated and included healthy healthcare staff and patients with a variety of diseases from bacterial pneumonia to lung cancer. Serological testing consisted of an enzyme linked immunosorbent assay designed to detect IgM and IgG antibodies against the N protein of SARS-CoV-2. Serial examination of COVID-19 patients resulted in IgM seroreactivity by day 4 post symptom onset, which peaked by day 9. In contrast, IgG sharply increased 12 days after symptom onset; all NAT positive patients were positive for IgG 30 days post symptom onset. In patients with suspected COVID-19 who tested NAT negative, IgM antibodies were detected in 87.5% and IgG was present in 70.8%. In contrast, only 3 individuals in the control group tested positive for IgG but IgM positivity was not observed. The authors calculated a sensitivity for diagnosis of COVID19 using IgM of 77.3% and a specificity of 100% while for IgG the sensitivity was higher at 83.3% and the specificity was 95%.