--when calcium levels have been recorded high in the past, but there is evidence of bone loss, to check the functioning of the parathryroid glands as well--these are the little glands embedded in the thyroid whose function is to regulate calcium metabolism.

It's certainly not uncommon, due to the action of medications or hyperplasia, for the parathyroids to produce too much hormone and cause blood levels of calcium to rise--and often, in response to the dysregulated hormone feedback, the body will leach calcium from bone to restore the serological balance. (And yes, this was me--despite all the weightlifting and such I do, at one point due to high parathyroid hormone I had high ionized calcium levels and a degree of osteopenia; last year I finally had surgery to remove two hyperplastic glands.)