Real-world assessment of Fluorecare SARS-CoV-2 Spike Protein Test Kit

OBJECTIVES: Since commercial SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) antigen rapid detection tests (Ag-RDTs) display broad diagnostic efficiency, this study aimed to evaluate the clinical performance of Fluorecare SARS-CoV-2 Spike Protein Test Kit in a real-life scenario. METHODS: The study population consisted of a series of patients undergoing SARS-Cov-2 diagnostic testing at Pederzoli Hospital of Peschiera del Garda (Verona, Italy). A nasopharyngeal swab was collected upon hospital admission and assayed with molecular (Altona Diagnostics RealStar(®) SARSCoV-2 RT-PCR Kit) and antigen (Fluorecare SARS-CoV-2 Spike Protein Test Kit) tests. RESULTS: The study population consisted of 354 patients (mean age, 47 ± 20 years; 195 women, 55.1%), 223 (65.8%) positive at molecular testing. A significant correlation was found between Fluorecare SARS-CoV-2 Spike Protein Test Kit and Altona (both S and E genes: r=−0.75; p<0.001). The cumulative area under the curve in all nasopharyngeal samples was 0.68. At ≥1.0 S/CO manufacturer’s cut-off, the sensitivity, specificity, negative and positive predictive values were 27.5, 99.2, 41.5 and 98.5%, respectively. Considerable improvement of sensitivity was observed as Ct values decreased, becoming 66.7% in samples with mean Ct values <30, 90.5% in those with mean Ct values <25, up to 100% in those with mean Ct values <20. CONCLUSIONS: The modest sensitivity and negative predictive value of Fluorecare SARS-CoV-2 Spike Protein Test Kit makes unadvisable to use this assay as surrogate of molecular testing for definitively diagnosing SARS-CoV-2 infection, though its suitable sensitivity at high viral load could make it a reliable screening test for patients with higher infective potential.