NEW YORK ─ Siemens Healthineers said on Thursday that its SARS-CoV-2 total antibody test was the only one of four assays in a head-to-head study that met Target Product Profile (TPP)-sensitivity criteria for immunoassays established by the UK Medicines and Healthcare products Regulatory Agency.
The comparison of four commercial immunoassays available in the UK for the detection of SARS-CoV-2 antibodies was published in a report commissioned by the UK Department of Health and Social Care and conducted by Public Health England, the University of Oxford, and Oxford University Hospitals NHS Foundation Trust.
Over three weeks in May and June, investigators evaluated Abbott’s SARS-CoV-2 Immunoassay, DiaSorin’s Liaison SARS-CoV-2 S1/S2 IgG, Roche’s Elecsys Anti-SARS-CoV-2, and the Siemens test.
The report said Abbott's assay had a sensitivity of 92.7 percent and specificity of 99.9 percent, DiaSorin's assay had a sensitivity of 95 percent and specificity of 98.6 percent, and Roche's assay had a sensitivity of 97.2 percent and specificity of 99.8 percent. All three assays met the TPP criteria for specificity but not sensitivity. Siemens' assay had a sensitivity of 98.1 and a specificity of 99.9 and met the criteria for both sensitivity and specificity.
According to the report, the investigators evaluated sensitivity using 536 positive samples from adults with a lab-confirmed SARS-CoV-2 infection, taken at equal to or greater than 20 days post-symptom onset. They evaluated specificity on 994 specimens from healthy adults collected before the pandemic.
The TPP for enzyme immunoassays requires a clinical sensitivity of greater than or equal to 98 percent in SARS-CoV-2-positive cases confirmed equal to or greater than 20 days after the appearance of first symptoms. It requires a clinical specificity of equal to or greater than 98 percent on samples collected greater than 6 months before the first identified cases of SARS-CoV-2 infection.
By optimizing assay thresholds to achieve a specificity of equal to or greater than 98 percent and extending the sample timeframe specification to equal to or greater than 30 days post-symptom onset, all four assays would meet the sensitivity criteria, the report said.
Patrick Barth, a Roche spokesperson, said in an email that the firm "welcomes the publication of this independent evaluation, which confirms that our antibody test is one of the most reliable on the market."
Basel, Switzerland-based Roche has evaluated its antibody test in 10,400 patient samples. The UK report is one of several evaluations that confirm its test is highly specific and sensitive, and reinforces its own study results, Barth said.
"Roche initially tested a total of more than 5,400 samples at a very early stage of the pandemic to develop a reliable antibody test at speed which demonstrates both clinical specificity and clinical sensitivity," he said. "Patients had a range of symptoms from mild to severe with a positive PCR test at least 14 days prior to the antibody test. This evaluation found that the test has a specificity greater than 99.8 percent and a sensitivity of 100 percent 14-days post-PCR confirmation."
An Abbott spokesperson said that its test has been evaluated in the scientific literature using more than 15,000 samples. For example, a large scale published research study on the test from the University of Washington found 99.9 percent specificity on 1,020 patient samples and 100 percent sensitivity on 689 samples when testing was conducted 17 days after symptoms began, the spokesperson said.
The Siemens Healthineers SARS-CoV-2 test identifies antibodies to a spike protein ─ also a focus of many vaccine studies ─ on the surface of the virus. Like the other assays in the study, it allows for the identification of patients who have developed an adaptive immune response, indicating prior exposure to COVID-19.
"High-quality antibody tests will be critical to successfully reopening economies across the globe," Deepak Nath, president of laboratory diagnostics at Siemens Healthineers, said in a statement. "Laboratories worldwide can be confident that our assay delivers the sensitivity and specificity we promised."