The clinical utility of SARS coronavirus-2 antibodies remains undefined. This case-control study aims to determine the clinical validity and utility of SARS-CoV-2 antibodies. The testing began using nucleic acid amplification test (NAAT) on nasopharyngeal swabs at the Johns Hopkins Hospital. The study involved 11,066 participants, out of which 115 (1%) were hospitalized adults investigated for COVID-19. A clinical record review was performed to classify them into a positive case group or a non–positive control group. Serum samples were then obtained for 18 repeatedly NAAT-negative patients i.e., 6 case-patients and 12 non–positive control patients. Antibodies were observed to be in 5 out of 6 case-patients, and none in the control group patients.

In conclusion, it is found that antibodies to SARS-CoV-2 show signs of infection when measured at least fourteen days after symptom onset, associate with clinical severity, and provide valuable diagnostic support in patients who are tested negative by NAAT but remain clinically suspicious for COVID-19. An accurate determination of infection time can rarely be proven, but its estimation by the time of symptom onset is revealed to be accurate and clinically applicable. As recently reported, IgM appears and wanes rapidly, limiting diagnostic utility and convalescent plasma donors’ appropriate characterization.