One of the key questions asked for a diagnostic assay is “is the performance good enough?” This question takes on forms such as: what should the performance goals be? How should they be evaluated? From a regulator’s point of view, there are two decisions that can be made:
Accept the assay – with the risk that patients may be harmed due to assay error
Reject the assay – with the risk that patients may be harmed due to the lack of information that would have been obtained by the assay
Now for any good assay, patients harmed from assay error is always extremely low (e.g., self justifying because it’s a good assay).
And a good assay provides important information to a clinician (e.g., self justifying because it’s a good assay). This also means that the lack of information from a rejected assay would likely cause great harm.
Hence the rational decision is always to approve an assay. Why doesn’t the FDA always approve assays? Perhaps because assays that harm patients are like a plane crash and no one likes plane crashes.