PTH and kidney failure: Serum PTH concentration is often increased in patients with hypercalcemia related to kidney failure, and these animals must be differentiated from those with primary HPTH.110,144 Serum iCa concentration is increased in primary HPTH but is usually normal or low in patients with CKD.110,209,227 Deleterious effects of hypercalcemia occur in patients with renal failure only if it is associated with increases in serum iCa concentration.