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Value of serologic assay in diagnosis of COVID-19 among patients with negative molecular assay

Aims and objectives: Due to the growing burden of coronavirus 2019 and considerable rate of RT-PCR false-negative results, a complementary diagnostic tool is necessary for the detection of active cases. Methods: This study was performed in Masih Daneshvari Hospital, Tehran, Iran, among admitted symptomatic cases clinically and radiologically suspected to COVID-19 and their first RT-PCR assay was negative. Results of second RT-PCR assay and serologic study were compared. Results: In the period of study 137 symptomatic patients with negative RT-PCR assay on the first sample were recruited. Second RT-PCR assay was positive for 45 (32.8%) of them. IgM and IgG antibodies against SARS-CoV-2 were positive in 83 (60.6%) and 86 (62.8%) of patients respectively. Finally, the serologic assay was diagnostic among 73% of patients and the yield of serology was higher after the first week of illness (p-value <0.001). The combination of RT-PCR and serology increased the diagnostic yield to 83.9%. Conclusions: This study showed that the serologic assay in parallel to RT-PCR may be useful as a complementary tool for diagnosis of COVID-19 among admitted cases.