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. 2022 Feb 16;60(5):771-777.
doi: 10.1515/cclm-2021-1142. Print 2022 Apr 26.

Ultrasensitive assay for saliva-based SARS-CoV-2 antigen detection

Annie Ren  1   2 , Dorsa Sohaei  1   2 , Antigona Ulndreaj  2 , Oscar D Pons-Belda  2 , Amaia Fernandez-Uriarte  2 , Ioannis Zacharioudakis  3 , George B Sigal  4 , Martin Stengelin  4 , Anu Mathew  4 , Christopher Campbell  4 , Nikhil Padmanabhan  4 , Daniel Romero  4 , Jessica Joe  4 , Antoninus Soosaipillai  5 , Vathany Kulasingam  1   6 , Tony Mazzulli  1   7 , Xinliu A Li  7 , Allison McGeer  1   7 , Eleftherios P Diamandis  1   2   6 , Ioannis Prassas  2   5
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Free article

Ultrasensitive assay for saliva-based SARS-CoV-2 antigen detection

Annie Ren et al. Clin Chem Lab Med. .
Free article

Abstract

Objectives: Widespread SARS-CoV-2 testing is invaluable for identifying asymptomatic/pre-symptomatic individuals. There remains a technological gap for highly reliable, easy, and quick SARS-CoV-2 diagnostic tests suitable for frequent mass testing. Compared to nasopharyngeal (NP) swab-based tests, saliva-based methods are attractive due to easier and safer sampling. Current saliva-based SARS-CoV-2 rapid antigen tests (RATs) are hindered by limited analytical sensitivity. Here, we report one of the first ultrasensitive, saliva-based SARS-CoV-2 antigen assays with an analytical sensitivity of <0.32 pg/mL, corresponding to four viral RNA copies/µL, which is comparable to that of PCR-based tests.

Methods: Using the novel electrochemiluminescence (ECL)-based immunoassay, we measured the SARS-CoV-2 nucleocapsid (N) antigen concentration in 105 salivas, obtained from non-COVID-19 and COVID-19 patients. We then verified the results with a second, independent cohort of 689 patients (3.8% SARS-CoV-2 positivity rate). We also compared our method with a widely used point-of-care rapid test.

Results: In the first cohort, at 100% specificity, the sensitivity was 92%. Our assay correctly identified samples with viral loads up to 35 CT cycles by saliva-based PCR. Paired NP swab-based PCR results were obtained for 86 cases. Our assay showed high concordance with saliva-based and NP swab-based PCR in samples with negative (<0.32 pg/mL) and strongly positive (>2 pg/mL) N antigen concentrations. In the second cohort, at 100% specificity, sensitivity was also 92%. Our assay is about 700-fold more sensitive than the Abbott Panbio Rapid Test.

Conclusions: We demonstrated the ultrasensitivity and specificity assay and its concordance with PCR. This novel assay is especially valuable when compliance to frequent swabbing may be problematic.

Keywords: SARS-CoV-2; electrochemiluminescence (ECL) immunoassay; mass testing; nasopharyngeal (NP) swab; saliva; sensitivity.

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