Abstract : Reverse transcription polymerase chain reaction (RT-PCR) was the gold standard confirmatory test for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which requires special facilities, and other reliable tests. The fluorescent immunoassay (FIA) biosensor antigen detects nucleoprotein SARS-CoV-2 viral in the early phase of acute infection, providing a cut-off index (COI) as a measure of the fluorescent signal. Both RNA dependent RNA polymerase (RdRp) and envelope (E) were specific markers for SARS-CoV-2. This research was a cross-sectional study design. The SD biosensor standard antigen F2400 analyzer was correlated with the target of RT-PCR WizDx™ CrystalMix RdRp and E SARS-CoV-2 genes. Secondary data collection from the FIA biosensor antigen and RT-PCR of the RdRp and E genes in January-July 2021 was carried out in February-March 2022. The correlation test of Fisher exact, contingency coefficient, and Spearman's rho used IBM SPSS Statistics 26 version. 100% Positive predictive RT-PCR was obtained at COI >10. The contingency coefficient of COI with RdRp and E genes were 0.560 and 0.533 (strong); the correlation coefficient with Ct values were -0.410 (moderate) and -0.398 (weak). There was a strong correlation between FIA biosensor antigen COI values with RT-PCR RdRp and E genes, but Ct values had a moderate and weak correlation.