J Clin Microbiol. 2021 Jan 19:JCM.02026-20. doi: 10.1128/JCM.02026-20. Online ahead of print.
Accurate diagnosis of acute severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) infection is critical for appropriate management of patients with this disease. We examined the possible complementary role of lab developed class-specific clinical serology in assessing SARS-CoV-2 infection in hospitalized patients. Serological tests for IgG, IgA, and IgM antibodies against the receptor binding domain (RBD) of SARS-CoV-2 were evaluated using samples from real time RT PCR (qRT-PCR)-confirmed in-patient COVID-19 cases. We analyzed the influence of timing and clinical severity on the diagnostic value of class-specific coronavirus disease 2019 (COVID-19) serology testing. Cross-sectional analysis revealed a higher sensitivity and specificity at lower optical density cutoffs for IgA in hospitalized patients when compared to IgG and IgM serology (IgG area under the curve (AUC): 0.91; 95%CI 0.89 to 0.93 vs. IgA AUC: 0.97; 95% CI 0.96 to 0.98 vs. IgM AUC: 0.95; 95% CI 0.92 to 0.97). The enhanced performance of IgA serology was apparent in the first two weeks after symptom onset and the first week after PCR testing. In patients requiring intubation, all three tests exhibit enhanced sensitivity. Among PCR-negative patients under investigation for SARS-CoV-2 infection 2 out of 61 showed clear evidence of seroconversion IgG, IgA and IgM. Suspected false-positive results in the latter population were most frequently observed in IgG and IgM serology tests. Our findings suggest the potential utility of IgA serology in the acute setting and explore the benefits and limitations of class-specific serology as a complementary diagnostic tool to PCR for COVID-19 in the acute setting.