ABSTRACT
INTRODUCTION: SARS-CoV-2 antigen tests can complement and substitute for RT-PCR tests. Centralized laboratory automated SARS-CoV-2 antigen tests that can be scaled to process a large number COVID-19 cases simultaneously are now available. We have evaluated the new Roche Elecsys SARS-CoV-2 antigen electro-chemiluminescent immunoassay. METHODS: The Roche SARS-CoV-2 antigen assay is a double-antibody sandwich electro-chemiluminescent immunoassay, which reports a cut-off index (COI) (COI ≥ 1.0 considered positive). We assessed assay precision and linearity, and confirmed the reactivity limit. We determined the assay sensitivity and specificity with a verification group (289 controls and 61 RT-PCR positive COVID-19 cases). Assay performance was also validated against the consecutive samples we received (7657 controls and 17 cases) for SARS-CoV-2 antigen testing from June to October 2021. RESULT: The assay had a within-run precision CV of 3.0% at COI 0.68, and a CV of 1.5% at COI 3.49. Between-run precision was 3.0% at COI 0.68 and 1.8% at COI 3.49. The assay was linear from COI 0.65 to 7.84. All 35 C50 ± 20% test results performed over 7 days were positive/negative, respectively. In the verification group, overall sensitivity was 42.6% (26/61 positive, 95% CI 30.0-55.9), and specificity was 99.7% (1/289 positive, 95% CI 98.1-100). The agreement between the SARS-CoV-2 antigen and the RT-PCR cycle threshold (Ct) count was good (r = 0.90). In cases with Ct counts ≤ 30, the antigen assay sensitivity improved to 94.7% (18/19 positive, 95% CI 74.0-99.9). In our validation group, antigen sensitivity was 62.5% (5/8 antigen positive, 95% CI 24.5-91.5) within the first week of disease onset, but no cases were reactive after the first week of disease onset. CONCLUSION: The Elecsys SARS-CoV-2 antigen assay has good performance within manufacturer specifications. The sensitivity of the Roche antigen assay was greatest when used in patients with lower RT-PCR Ct values (≤30) and within the first week of disease onset.
ABSTRACT
Early and accurate detection of SARS-CoV-2 is important for diagnosis and transmission control. The use of high-throughput and automated testing allows laboratories to better deliver diagnostic testing given manpower and resource limitations. We validated the clinical and analytical performance of the Hologic Panther Aptima SARS-CoV-2 assay with an emphasis on detection of specimens with low viral loads. The clinical performance was evaluated using 245 clinical specimens, against a comparator PCR-based laboratory developed test (LDT). The analytical performance was determined by replicate testing of contrived samples in a ten-fold dilution series (CT values 32-42, based on LDT). The Aptima assay had 96.7% overall percent agreement, 100% negative percent agreement and 88.1% positive percent agreement. It was able to consistently detect SARS-CoV-2 in contrived samples with CT = 32 by LDT (calculated 2354 copies/mL). The 95% limit of detection of the Aptima assay was estimated to be at LDT CT = 33 (equivalent to 870 copies/mL). The relative light units (RLU) × 1000 for 52 true positive clinical specimens was 962.2 ± 181.5, and that for the 186 true negative specimens was 264.6 ± 14.3. The Aptima assay was a reliable method with a high overall percent agreement against our comparator LDT. We propose that samples reported as negative by the Aptima assay with RLU > 350 be tested by a secondary method, in order to improve detection of samples with very low viral loads.