Clinical Evaluation of the Rapid STANDARD Q COVID-19 Ag Test for the Screening of Severe Acute Respiratory Syndrome Coronavirus 2

Standard tests for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) detect the presence of viral RNA using real-time reverse transcription (rRT)-PCR. Recently, convenient, rapid, and relatively inexpensive SARS-CoV-2 antigen (Ag) detection methods have been developed. The STANDARD Q COVID-19 Ag test (SD Biosensor, Inc., Suwon, Korea) is a rapid immunochromatography test that qualitatively detects the nucleocapsid protein of SARS-CoV-2 using gold conjugated antibodies. We evaluated its performance in comparison with that of Allplex 2019-nCoV Assay (Seegene, Seoul, Korea) in a retrospective case-control study using residual samples. The sensitivity and specificity of the STANDARD Q COVID-19 Ag test were 89.2% (58/65) and 96.0% (96/100), respectively. Cycle threshold (Ct) values for the three target SARS-CoV-2 genes (envelope, RNA-dependent RNA polymerase, and nucleocapsid genes) included in Allplex 2019-nCoV Assay were significantly lower in Ag test-positive patients than in Ag test-negative patients (P<0.001). The Ag test sensitivity was higher in samples with Ct≤30 and those collected one to five days post symptom onset. In conclusion, the STANDARD Q COVID-19 Ag test can serve as an alternative in high-prevalence settings, when the low sensitivity is compensated or when rRT-PCR tests are limited.