Comparison of Allplex™ SARS-CoV-2 Assay, Easy SARS-CoV-2 WE and Lumipulse quantitative SARS-CoV-2 antigen test performance using automated systems for the diagnosis of COVID-19

Abstract

Diagnostic methods based on SARS-CoV-2 antigen detection are a promising alternative to SARS-CoV-2 RNA amplification. We evaluated the automated chemiluminescence-based Lumipulse® G SARS-CoV-2 Ag assay as compared to real time assays (combined results from RT-PCR Allplex™ SARS-CoV-2 assay and Easy SARS-CoV-2 WE kit) on 513 nasopharyngeal swabs (NPS). Among these, 53.6% resulted positive to RT-PCR, considered as the reference test. Compared to the reference test, overall sensitivity and specificity of Lumipulse® G SARS-CoV-2 Ag assay were 84.0%, and 89.1%, respectively, and overall agreement between the antigen and molecular assays was substantial (κ = 0.727). When stratifying samples into groups based on ranges of RT-PCR cycle threshold (Ct), the antigen test sensitivity was >95% for samples with Ct <30. Linear regression analysis showed strong and highly significant correlation between the Lumipulse Ag concentrations and the RT-PCR Ct values (RdRp gene), irrespective of whether the Ct values from molecular test were combined in a unique regression analysis or analysed separately. Overall, chemiluminescence-based antigen assay may be reliably applied to NPS samples to identify individuals with high viral loads, more likely to transmit the virus.

Keywords: Antigen assay; COVID-19; Lumipulse; RT-PCR; SARS-CoV-2.

Figure 1

(A) SARS-CoV-2 N antigen concentration in 257 samples positive to the Lumipulse® G SARS-CoV-2 Ag assay, grouped according to the number of genes resulted positive by RT-PCR: confirmed with complete set of genes, i.e. to 3 genes with the Allplex™ SARS-CoV-2 assay and to 2 genes with the Easy SARS-CoV-2 WE assay (median: 3.11 Log pg/mL); confirmed with incomplete set of genes, i.e. to 2 genes with the Allplex™ SARS-CoV-2 assay and to 1 gene with the Easy SARS-CoV-2 WE assay (median: 0.57 Log pg/mL); not confirmed (median: 0.28 Log pg/mL). Statistically significant differences in Student´s T test are indicated in the figure. (B) Correlation between Lumipulse Ag concentrations (Log pg/mL) and Ct values of RdRp gene from the RT-PCR combined results of Allplex™ SARS-CoV-2 Assay and Easy SARS-CoV-2 WE kit (n=513). (C and D) Correlation between Lumipulse Ag concentrations (Log pg/mL) and Ct values of RdRp gene split for from the Allplex™ SARS-CoV-2 Assay (n=387, C) and for the Easy SARS-CoV-2 WE kit (n=126, D). Samples with Ct <40 or pg/mL ≥1.34pg/mL were considered positive. For statistical calculations, an arbitrary value of 41 Ct was assigned to all RT-PCR negative samples and an arbitrary value of 1.0 pg/mL was assigned to all samples with Ag concentration <1.0 pg/mL.