PTH and Hypercalcemia: However, diagnosis of IHC is a process of exclusion and most often requires the analysis of phosphorus and calcium metabolic hormones, including PTH, PTH‐related peptide (PTHrp), 25‐hydroxyvitamin D and 1,25‐dihydroxyvitamin D, to eliminate primary or tertiary hyperparathyroidism, malignancy‐associated hypercalcemia, or vitamin D toxicity.22, 23, 24