The European Commission's Medical Device Coordination Group has provided guidance on the minimum requirements for rapid COVID-19 antibody tests.
Antibody tests of questionable accuracy proliferated on both sides of the Atlantic early in the pandemic, leading the U.S. and European Union to try to raise standards. The guidance from MDCG sets out what is expected of tests sold in the EU.
MDCG expects antibody tests to achieve at least 98% specificity. The group said it is hard to set a minimum value for sensitivity but noted the World Health Organization puts the bar at 90%.
The outgoing in vitro diagnostic directive that applies to rapid antibody tests requires that products are suitable for their intended purpose taking into account the “generally acknowledged state of the art.” In that legal context, “state of the art” refers to what is achievable by most devices. The problem in the COVID-19 antibody space is it is somewhat unclear what is achievable by most devices.
MDCG created the guidance to bring clarity to that point. In doing so, MDCG aims to set a minimum standard for rapid antibody tests sold in the EU and articulate what it expects of manufacturers.
After reviewing the literature, MDCG set the minimum diagnostic specificity at 98%. Test developers should assess the specificity of their tests on a panel of least 200 samples either collected prior to November 2019 or confirmed as negative. The people who provided the samples should be broadly representative of the target population for the test.
MDCG was vaguer about the minimum sensitivity, explaining figures cited in the instructions for use it reviewed “were heterogeneously determined, making it difficult to conclude on a minimum value reflecting the state of the art for this performance.” The group noted that sources including WHO “generally require at least 90% diagnostic sensitivity for each antibody type.”
Again, MDCG expects test developers to assess the sensitivity of their tests on at least 200 samples. The samples should come from people with confirmed SARS-CoV-2 infections and be accompanied by details of the timing between sampling and the onset of symptoms. MDCG expects developers to use samples from patients at different times and disease severity as “diagnostic sensitivity depends highly on the time interval between the contact with the virus and sample taking.”
MDCG is providing some flexibility in how developers validate test sensitivity. Developers can use samples taken from the same individual at different times. In other cases, developers may be allowed to use a test “in parallel with an established device to investigate a representative set of samples, without preselection or exclusion of specimens, from a high incidence situation such as from a local or regional outbreak or from hospitals."