A comparative assessment of the performance of 4 widely available antibody immunoassays and 1 novel immunoassay showed that these assays can be used for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serologic testing to achieve sensitivity and specificity of at least 98%, according to study results published in The Lancet Infectious Diseases.1
Study authors conducted a head-to-head assessment of the following 4 commercial antibody assays, with the aim of evaluating the performance of each assay:
- SARS-CoV-2 IgG assay (Abbott, Chicago, IL, USA)
- LIAISON SARS-CoV-2 S1/S2 IgG assay (DiaSorin, Saluggia, Italy)
- Elecsys Anti-SARS-CoV-2 assay (Roche, Basel, Switzerland)
- SARS-CoV-2 Total assay (Siemens, Munich, Germany)
The Abbott and Roche assays are known to detect antibodies to the nucleoprotein, whereas the DiaSorin and Siemens assays detect antibodies to the spike glycoprotein. The Abbott and Diasorin assays detect immunoglobulin (Ig)G only, whereas the Roche and Siemens assays detect total antibody. Study authors compared these 4 assays and a novel 384-well ELISA (the Oxford immunoassay) that detects total IgG to a trimeric spike protein.
Sensitivity and specificity were derived from 976 pre-pandemic blood samples from research studies in Oxford, United Kingdom and 536 blood samples from patients with laboratory-confirmed SARS-CoV-2 infection. Assay performance was also assessed according to the sampling timepoint (defined as days after symptom onset and post reverse transcription polymerase chain reaction test) at intervals of 14 days or more (according to original protocol), 20 days or more (according to the UK Medicines and Healthcare products Regulatory Agency), and 30 or more days.
All assays were found to have a high sensitivity (92.7%-99.1%) and specificity (98.7%-99.9%). Only the Siemens assay and the Oxford immunoassay met the specificity and sensitivity target of at least 98% using the predefined assay thresholds, achieving this threshold at all 3 timepoints assessed (≥14, ≥20, and ≥30 days after symptom onset). The Roche assay met the specificity and sensitivity target of at least 98% on samples taken at least 30 days after symptom onset and could potentially meet the sensitivity and specificity targets on samples taken at least 14 and 20 days after symptom onset by threshold adjustment. Study authors noted that the thresholds for the Abbott and DiaSorin assays could be optimized to achieve sensitivity and specificity of at least 98% on samples taken at least 30 days after symptom onset (but not ≥14 or ≥20 days after symptom onset). Only 3 samples did not give rise to any detectable antibody responses among the 5 assays.
Despite the ability to achieve sensitivity and specificity of at least 98%, the differences observed in assay performance would translate into thousands of additional incorrect diagnoses between the worst and best assays, if millions of tests were done in large populations. For example, at a 10% seroprevalence, the Siemens assay would generate an estimated 2800 total errors per million tests, whereas the DiaSorin assay would generate an estimated 16,700 total errors per million tests.
“These assays are impractical to deploy at scale,” Catherine F. Houlihan, from University College London Hospitals, and Rupert Beale, from the Francis Crick Institute in London, UK, noted in an editorial commentary.2 They also noted that different assays would probably be used to answer specific questions. For instance, most vaccine candidates elicit responses to spike protein rather than nucleocapsid protein.
“Measuring antibodies to spike will therefore indicate whether there has been a good response, whereas measuring antibodies to nucleocapsid would help identify whether the individual had nonetheless become infected,” they added. “Further work is required to investigate what titer of neutralizing antibodies correlates with protection, how long neutralization activity persists, and which assay best predicts that,” and that the “possibility of a one-size-fits-all immunological assay looks less and less likely,” Houlihan and Beale concluded.
While researchers did not observe any significant differences in assay sensitivity by disease severity, this subgroup analysis was constrained by small numbers. Other limitations included incomplete data on sex, age, and immunocompromised status.
Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.
1. National SARS-CoV-2 Serology Assay Evaluation Group. Performance characteristics of five immunoassays for SARS-CoV-2: a head-to-head benchmark comparison. Lancet Infect Dis. Published online September 23, 2020. doi:10.1016/S1473-3099(20)30634-4
2. Houlihan CF, Beale R. The complexities of SARS-CoV-2 serology. Re: Performance characteristics of five immunoassays for SARS-CoV-2: a head-to-head benchmark comparison. Lancet Infect Dis. Published online September 23, 2020. doi:10.1016/S1473-3099(20)30699-X