Italian 
English Clinical assessment of FREND COVID-19 Ag test in an unselected population referred for routine SARS-CoV-2 testing
AUTORI
1Section of Clinical Biochemistry, University of Verona, Verona, Italy
2Service of Laboratory Medicine, Pederzoli Hospital, Peschiera del Garda, Italy
3Medical Direction, Pederzoli Hospital, Peschiera del Garda, Italy
4The Heart Institute, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA
@equally contributed to this work
ABSTRACT
Background: this observational retrospective study was aimed at evaluating the clinical performance of the novel microfluidic fluorescence immunoassay FREND COVID-19 Ag test in a population of unselected individuals undergoing routine SARS-CoV-2 (severe acute respiratory coronavirus 2) testing.
Methods: the study population consisted of a series of outpatients referred to the Service of Laboratory Medicine of Pederzoli Hospital (Peschiera del Garda, Verona, Italy) between April 12 and 30, 2021, for SARS-CoV-2 testing for being either symptomatic or having had close contact with one or more COVID-19 cases. A routine nasopharyngeal sample was collected at hospital admission and analyzed with both molecular (Altona Diagnostics RealStar® SARS-CoV-2 RT-PCR Kit) and antigen (FREND COVID-19 Ag) tests.
Results: the area under the curve (AUC) of FREND COVID-19 Ag in all nasopharyngeal samples compared to molecular testing was 0.69 (95%CI, 0.64-0.75). At the ≥1.0 TCID50/mL manufacturer’s cut-off, accuracy, sensitivity, specificity, negative (NPV) and positive (PPV) predictive values were 61.3%, 0.27, 1.00, 0.55 and 1.00, respectively. The AUC of FREND COVID-19 Ag in samples with cycle threshold (Ct) values of both SARS-CoV-2 S and E genes <29.5 was 1.00. At ≥1.0 TCID50/mL (median tissue culture infective dose per mL) manufacturer’s cut-off, accuracy, sensitivity, specificity, NPV and PPV values were 99.2%, 1.00, 0.99, 1.00 and 0.95, respectively.
Conclusions: FREND COVID-19 Ag could not replace routine molecular testing for achieving a definitive diagnosis of SARS-CoV-2 infection, but can be used as a surrogate test for identifying patients with higher nasopharyngeal viral load and thus greater infectious potential.