While the US FDA’s most notable act regarding Covid-19 tests last week was to remove a previously authorised one from market, it is still granting emergency use authorisations to new diagnostics. Over the past week one antibody and four molecular tests – excluding those developed by academic and non-profit groups – have been authorised by the regulator. The antibody test is Biohit Healthcare’s immunochromatographic Sars-CoV-2 IgM/IgG assay, which has, according to its instructions for use, undergone independent validation testing sponsored by the National Cancer Institute. This evaluation concluded that the Finnish group’s assay has sensitivity and specificity for the two immunoglobulins combined of 96.7% and 95.0%, respectively. At Covid-19’s estimated prevalence of 5%, this translates into positive and negative predictive values of 50.4% and 99.8%. This might indicate that the FDA is willing to tolerate quite a low PPV, but this is not unreasonable – it is NPV that is the vital point.
Note: "Other" includes one antigen test, one home sampling kit and one IL-6 test.