Evaluation and Validation of the Roche Elecsys SARS-CoV-2 Antigen Electro-Chemiluminescent Immunoassay in a Southeast Asian Region

Chin Shern Lau; Soon Kieng Phua; See Ping Hoo; Boran Jiang; Tar-Choon Aw

doi:10.3390/vaccines10020198

Evaluation and Validation of the Roche Elecsys SARS-CoV-2 Antigen Electro-Chemiluminescent Immunoassay in a Southeast Asian Region

Vaccines (Basel). 2022 Jan 27;10(2):198. doi: 10.3390/vaccines10020198.

Authors

Chin Shern Lau¹, Soon Kieng Phua¹, See Ping Hoo¹, Boran Jiang^{1

2}, Tar-Choon Aw^{1

3

4}

Affiliations

¹ Department of Laboratory Medicine, Changi General Hospital, Singapore 529889, Singapore.
² Department of Microbiology, Changi General Hospital, Singapore 529889, Singapore.
³ Department of Medicine, National University of Singapore, Singapore 119077, Singapore.
⁴ Academic Pathology Program, Duke-NUS Medical School, Singapore 169857, Singapore.

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.

Keywords: COVID-19; RT-PCR; SARS-CoV-2; antigen; central laboratory testing.