Performance Evaluation of Instrument-Based SARS-CoV-2 Rapid Antigen Fluorescent Immunoassays for Point-of-Care Detection

Rapid antigen tests targeting SARS-CoV-2 nucleocapsid protein were essential for decentralised testing during the COVID-19 pandemic. Independent performance evaluations are critical to guide regulatory approval and implementation, particularly in resource-limited settings. This study presents a retrospective analytical and operational evaluation of two instrument-based fluorescent immunoassays (FIA): the PCL COVID-19 Ag Rapid FIA (PCL Inc., South Korea) and LumiraDx SARS-CoV-2 Ag Test (LumiraDx Ltd., UK). Analytical sensitivity was determined using recombinant nucleocapsid protein and viral cultures. Clinical performance was assessed using residual clinical specimens (n=110) with RT-PCR as reference, stratified by cycle threshold (Ct). Operational characteristics were assessed using a structured Likert framework. Overall sensitivity was 63% (51-73) for PCL and 95% (88-99) for LumiraDx. For Ct≤25, sensitivity increased to 93% and 100%. Specificity was ≥97% for both. LumiraDx maintained sensitivity (83-94%) at Ct 25-30, whereas PCL detected no positives in this range. Limit of detection was 0.039 nM (PCL) and 0.6 pM (LumiraDx). Operational usability was high for both (90% PCL, 87% LumiraDx). LumiraDx showed higher analytical sensitivity across a broader viral load range, supporting primary diagnostic use, whereas PCL was limited to high viral loads. This provides a reproducible framework for rapid diagnostic assessment during emerging outbreaks.