Clinical Assessment of the DiaSorin LIAISON SARS-CoV-2 Ag Chemiluminescence Immunoassay

Background: Due to the large volume of tests needed in a relatively short time for screening and diagnosing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, antigen immunoassays may provide a potential supplement to molecular testing. This study was aimed to assess the clinical preference of DiaSorin LIAISON SARS-CoV-2 Ag chemiluminescence immunoassay. Methods: An upper respiratory specimen was collected in a series of patients referred to the Laboratory Medicine service of Pederzoli Hospital (Peschiera del Garda, Verona, Italy) for screening or diagnosis of SARS-CoV-2 infection. Nasopharyngeal samples were assayed with DiaSorin LIAISON SARS-CoV-2 Ag test and Altona Diagnostics RealStar® SARS-CoV-2 RT-PCR Kit. Results: The final study population consisted of 421 patients (median age, 48 years; 227 women), 301 (71.5%) with positive result of molecular testing, and 126 (29.9%) with cycle threshold (Ct) values of both E and S genes <29.5, thus reflecting higher infectivity. The area under the curve of DiaSorin LIAISON SARS-CoV-2 Ag test 0.82 (95% CI, 0.79-0.86) for sample positivity and 0.98 for higher sample infectivity (95% CI, 0.97 to 0.99). The optimal cut-off for sample positivity was 82 TCID50/mL (0.78 sensitivity, 0.73 specificity and 77% diagnostic accuracy), whilst that for identifying samples associated with a high infective risk was 106 TCID50/mL (0.94 sensitivity, 0.96 specificity and 95% diagnostic accuracy). Conclusion: The performance of this chemiluminescence immunoassay would not permit it to replace molecular testing for diagnosing SARS-CoV-2, but may enable rapid and efficient detection of subjects with high SARS-CoV-2 viral load, who are responsible for the largest proportion of infectious clusters.