Another bizarre coincidence - I was just asked if I should see a patient with ESRD, normal calcium and mildly elevated PTHrP (sent in the setting of calcium that was high once a few months ago, although subsequently the calcium normalized and ionized calcium is also normal) without any evidence of malignancy clinically.
Anyway, I looked into it and most labs doing PTHrP tests will use a C-terminal assay which can be elevated in pts with CKD; an N-terminal assay will apparently be normal (
citation).
Whether I'll be able to actually find a lab that can run this test is another question, but at least I feel like in my patient's case, the ESRD is a decent enough explanation.