In the Race for Home-Based Rapid COVID Tests, Antibody Tests Show Promise
[Thursday, May 28, 2020]
Tests that detect antibodies to the coronavirus in blood, serum and plasma have emerged as the key players in creating a feel-safe environment for re-opening our lives post-pandemic, and present an interesting safety and effectiveness paradigm for regulatory agencies. Antibody detecting tests can be designed to give results in minutes, do not require sophisticated equipment or extensive training, and are inexpensive making it possible to deploy on massive scales. But they do not detect the infection, only past or recent exposure to the virus. It takes several days post-infection for the antibodies to appear in the blood of the infected individual, and usually antibodies stay much after the infection has subsided. Lack of antibodies in the blood could indicate either that the infection is very recent, or that there is no infection. This can be verified by repeated testing every few days. Some tests can distinguish between IgM antibodies, that appear early in the infection, from IgG antibodies that appear later in the infection and stick around post-infection, making it possible to roughly track the progress of the infection. Due to the inherent limitations of these tests, regulatory agencies worldwide, FDA included, do not accept antibody detection tests as a diagnostic for the active infection, although it is universally accepted that these tests do not present any safety issue and may provide some benefit of knowing if an individual carries antibodies to the virus. Also, these tests present the best promise for rapid home-based tests which cannot be feasible with PCR and antigen-detecting ELISA tests. So, FDA allowed initially these tests without much review to be used only for screening populations. Due to the ease of developing such tests, hundreds of such tests were developed within weeks of the pandemic, and allowed to be sold with limited oversight creating confusion for patients and physicians alike. FDA revised its policy to control the unregulated, allowed tests but has so far allowed these tests to the marketed without formal authorization. FDA intended to create a “feel-safe” environment quickly while avoiding false promise. In a pandemic, it is about “feeling safe”, and not just “being safe”. Large-scale, rapid, easy, and inexpensive tests create that even when there are disclaimers warning the users of the limitations of these tests. This is a case of FDA balancing strict interpretation of the scientific utility of a product with the practical necessity of the times where diagnostic tests with limited potential can do better than tests with more certainty but practical limitations.