Detection of SARS-CoV-2 N-antigen in blood during acute COVID-19 provides a sensitive new marker and new testing alternatives

ObjectivesMolecular assays on nasopharyngeal swabs remain the cornerstone of COVID-19 diagnostics. The high technicalities sampling and molecular assays, as well scarce resources reagents, limit our testing capabilities. Several strategies failed, to date, fully alleviate this process (e.g. saliva or antigen samples). We assessed clinical performances SARS-CoV-2 nucleocapsid (N-antigen) ELISA detection in serum plasma using Quantigene® (AAZ, France) assay.MethodsPerformances were determined 63 samples from non-COVID patients 227 (165 patients) French COVID CoV-CONTACT cohorts with RT-PCR-confirmed infection, including 142 (114 obtained within 14 days after symptom onset.ResultsSpecificity was 98.4% (95% CI 95.3–100). Sensitivity 79.3% overall (180/227, 95% CI, 74.0–84.6) 93.0% (132/142, 88.7–97.2) onset. Ninety-one included had collected same 24 hr. Among those viral loads, i.e. Ct value below 30 33, only 1/50 4/67 tested negative for N-antigenaemia, respectively. a RT-PCR, 8/12 presented positive N-antigenaemia; lower respiratory tract explored six these eight patients, showing RT-PCR five cases.DiscussionThis is first evaluation commercially available N-antigen assay. It presents robust specificity sensitivity symptoms This approach provides valuable new option diagnosis, requiring blood draw easily scalable all laboratories.