SARS-CoV-2 rapid antigen test in comparison to RT-PCR targeting different genes: A real-life evaluation among unselected patients in a regional hospital of Italy

Abstract

We assessed the performance of the Panbio rapid antigen detection (RAD) test for the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and we compared it with the routine reverse transcriptase-polymerase chain reaction (RT-PCR)-based molecular test in a population of 4167 unselected patients admitted to IRCCS Sacro Cuore Don Calabria Hospital. Analysis stratified by cycling threshold (C_t ) value of SARS-CoV-2 gene targets indicated that antigen (Ag)-positive C_t values were significantly lower compared to Ag-negative values (p < 0.0001). Overall, we found discordance in 140, tested negative by RAD and positive by RT-PCR, and in 4 resulted positive by RAD and negative by RT-PCR. RAD test achieved a sensitivity and specificity of 66.82% and 99.89%, respectively. The positive predictive value was shown to be 97.87% while the negative predictive value was shown to be 97.62%. In our context, the RAD test showed a reliable diagnostic response in subjects that displayed high C_t values, corresponding to high viral load, while low ability was displayed to identify positive cases with medium-low C_t values, thus presenting low viral load and where confirmatory RT-PCR was needed. Our finding supports the use of the RAD test in real-life settings where a high volume of swabs is being processed but with caution when interpreting a positive test result in a low prevalence setting.

Keywords: Panbio™ COVID-19; RAD; RT-PCR; SARS-CoV-2.

FIGURE 1

(A) Distribution of C _t values by RAD tested positive and negative. Statistical analysis was performed by Student's t‐test (***p < 0.0001). (B, C) C _t values in RAD+/RT‐PCR+ and in RAD−/RT‐PCR+ specimens, respectively. Data are presented as box and whisker plots, showing median (horizontal line), boxes representing the 25th to 75th percentiles, whiskers representing minimum and maximum values. ***p < 0.001, **p < 0.001 was determined by one‐way ANOVA. ANOVA, analysis of variance; RAD, rapid antigen detection; RT‐PCR, reverse transcriptase‐polymerase chain reaction

FIGURE 2

Comparison of C _t values of SARS‐CoV‐2 RT‐PCR gene targets according to RAD result. Each dot plot represents an individual C _t value. One‐way ANOVA was performed (***p < 0.0001). ANOVA, analysis of variance; RAD, rapid antigen detection; RT‐PCR, reverse transcriptase‐polymerase chain reaction; SARS‐CoV‐2, severe acute respiratory syndrome coronavirus 2