Comparative analysis of antigen and molecular tests for the detection of Sars-CoV-2 and related variants: a study on 4266 samples

Caputo, Valerio; Bax, Cristina; Colantoni, Luca; Peconi, Cristina; Termine, Andrea; Fabrizio, Carlo; Calvino, Giulia; Luzzi, Laura; Panunzi, Giorgia Gaia; Fusco, Claudia; Strafella, Claudia; Cascella, Raffaella; Battistini, Luca; Caltagirone, Carlo; Salvia, Antonino; Sancesario, Giulia; Giardina, Emiliano

Objectives The present study compared the performance of Lumipulse G Sars-CoV-2 Ag kit with TaqPath COVID-19 RT-PCR CE IVD kit. Methods The study was conducted on 4266 naso-oropharyngeal swabs. Samples were subjected to antigen RT-PCR tests for detection of Sars-CoV-2 and related variants. Statistical analyses were conducted in R software. Results We found 503 positives (including 138 H69-V70 deletion carriers) and 3763 negatives by RT-PCR, whereas 538 positives and 3728 negatives were obtained by antigen testing. We achieved empirical and binormal AU-ROCs of 0.920 and 0.990, accuracy of 0.960, sensitivity of 0.866, specificity of 0.973, positive and negative predictive values of 0.810 and 0.980. We obtained a positive correlation between viral loads and antigen levels (R2 = 0.81), founding a complete concordance for high viral loads (log10copies/mL>5.4). Antigen levels >222 pg/mL were found to be reliable in assigning positive samples (p < 0.01). Concerning variant carriers, antigen test detected them with the same accuracy of other positive samples. Conclusions Molecular and antigen tests should be evaluated regarding the prevalence of the area. In case of low prevalence, antigen testing can be employed as a first-line screening for the timely identification of affected individuals with high viral load, also if carriers of Sars-CoV-2 variants.