An international team of experts conducted a multi-laboratory evaluation of 21 commercial high-throughput assays used in laboratories to determine whether someone has antibodies to SARS CoV-2 proteins, using 1,000 blood-donor samples. CITF Testing Working Party Lead Dr. Mel Krajden and Testing Working Party member Dr. Steven Kleinman were among the experts involved.

Some assays recognized all possible antibodies (total Ig assays), while others recognized only individual antibody types (e.g., IgG or IgA). Some assays detected antibodies recognizing spike (anti-S) proteins, while others recognized the nucleocapsid (anti-N). Some assays recognized antibodies against multiple targets; for example, assays from DZ-Lite SARS and Bio-Rad detected antibodies recognizing either S or N proteins.

Key points:

  • The assays were very good at correctly identifying negative samples (otherwise known as test specificity), i.e., identifying between 96% to 100% of all negatives, depending on the assay. Most assays (13/20) had specificities above 99%, and 5/20 assays had specificities of 100%.
  • Some assays were less accurate at correctly diagnosing a positive result (otherwise known as test sensitivity). Most assays (17/20) had sensitivities greater than 80%. The lowest sensitivity was noted for EUROIMMUN IgA assay (only 63% of the positive samples returned positive results on the assay), while the highest was noted for Ortho VITROS Total Ig anti-S, where as many as 96% of the positive samples were correctly recognized.

The length of time for which antibodies were detected also varied among the assays. In general, assays that measured either total Ig or just IgG antibodies recognizing spike proteins could detect antibodies for a longer period after infection than assays that measured antibodies recognizing nucleocapsid proteins. For example, the Abbott and EUROIMMUN IgG anti-N assays detected antibodies in less than 70% of specimens collected over 90 days post symptoms onset, while total Ig assays like the Ortho Vitros anti-S total Ig and Roche Elecsys anti-N total Ig assays detected antibodies in 100% of specimens at these timepoints.

While assays with high sensitivity, specificity and durable antibody detection are ideal for serosurveillance Serosurveillance monitors and estimates antibody levels in blood samples from certain groups of people against infectious agents, such as SARS-CoV-2, the virus that causes COVID-19.”, less sensitive assays could have other applications such as characterizing antibody responses after infection and vaccination as well as detection of breakthrough infections Breakthrough infection occurs when individuals fully vaccinated against a disease, such as COVID-19, are subsequently infected with the agent causing that disease, such as SARS-CoV-2. The term ‘breakthrough’ signifies the infectious agent broke through the protective barrier the vaccines provide..

The study provided performance data relevant to serological testing that will allow clinicians, public health organizations, laboratorians, and emergency response planners to determine which assay would best fit their needs.

 

Stone M, Grebe E, Sulaeman H, Di Germanio C, Dave H, Kelly K, Biggerstaff B, Crews BO, Tran N, Jerome KR, Denny TN, Hogema B, Destree M, Jones JM, Thornburg N, Simmons G, Krajden M, Kleinman S, Dumont LJ, Busch MP. Evaluation of commercially available high-throughput SARS-CoV-2 serological assays for serosurveillance and related applications. medRxiv doi: 10.1101/2021.09.04.21262414