Quote Originally Posted by BazzaS View Post
Yes. (For both vitamin D, and iron).

For the initial “working out is there a problem”, Vitamin D levels would have had to be specifically requested (it isn’t a “routine test”), while iron deficiency would be hinted at by a particular type of anaemia.

That anaemia would be detectable on a routine ‘full blood count’ (which would show a “microcytic anaemia”, which they would then look further into, iron deficiency being the most common cause of one subset of microcytic anaemia).
They wouldn’t actually monitor “iron levels” (by measuring the amount of iron) though, using a surrogate marker (ferritin) instead.
This is a Pulse article on Vit D from 2013.