Lumipulse G SARS-CoV-2 Ag Assay Evaluation for SARS-CoV-2 Antigen Detection Using 594 Nasopharyngeal Swab Samples from Different Testing Groups

Menchinelli, G.; Bordi, L.; Marzialiotti, F.; Palucci, I.; Capobianchi, M. R.; Sberna, G.; Lalle, E.; Romano, L.; De Angelis, G.; Marchetti, S.; Sanguinetti, M.; Cattani, P.; Posteraro, B.

Compared to RT-PCR, lower performance of antigen detection assays, including the Lumipulse G SARS-CoV-2 Ag assay, may depend on specific testing scenarios. We tested 594 nasopharyngeal swab samples from individuals with COVID-19 (RT-PCR cycle threshold [Ct] values [≤]40) or non-COVID-19 (Ct values [≤]40) diagnoses. RT-PCR positive samples were assigned to diagnostic, screening, or monitoring groups of testing. With a limit of detection of 1.2 x 104 SARS-CoV-2 RNA copies/ml, Lumipulse showed positive percent agreement (PPA) of 79.9% (155/194) and negative percent agreement of 99.3% (397/400), whereas PPAs were 100% for samples with Ct values of <18 or 18-<25 and 92.5% for samples with Ct values of 25-<30. By three groups, Lumipulse showed PPA of 87.0% (60/69), 81.1% (43/53), or 72.2% (52/72), respectively, whereas PPA was 100% for samples with Ct values of <18 or 18-<25, and was 94.4%, 80.0%, or 100% for samples with Ct values of 25-<30, respectively. RT-PCR positive samples were also tested for SARS-CoV-2 subgenomic RNA and, by three groups, testing showed that PPA was 63.8% (44/69), 62.3% (33/53), or 33.3% (24/72), respectively. PPAs dropped to 55.6%, 20.0%, or 41.7% for samples with Ct values of 25-<30, respectively. All 101 samples with a subgenomic RNA positive result had a Lumipulse assays antigen positive result, whereas only 54 (58.1%) of remaining 93 samples had a Lumipulse assays antigen positive result. In conclusion, Lumipulse assay was highly sensitive in samples with low RT-PCR Ct values, implying repeated testing to reduce consequences of false-negative results.