Comment:

I like the idea of offering two ways of doing it. But in the laboratory, the example you gave doesnt happen. If they cant make a call, they will almost always include it in the answer. If the specimen was inadequate in volume or otherwise not usable, they MIGHT also say that in the valuebut more often, that will be a comment in the data absent reason.

There is a more common reason for data being absent. In urinalyses and differential cell counts, they only report values > 0 . In the case that values<0, they just dont send a record. You might want to mention that case, so that naïve implementers dont think it has to fall into one of the two cases you present.

Summary:

absent data example