Hypocalcemia may also occur because of acute or chronic hyperphosphatemia. Plasma phosphate, when elevated, complexes with calcium to cause subsequent extraskeletal calcifications; if chronically maintained, this elevation depresses renal 1α-hydroxylase activity and leads to reduced production of 1,25(OH)₂D. Hyperphosphatemia may result from iatrogenic administration of phosphate (either parenterally, orally, or rectally) or release from cells (e.g., after rapid tumor lysis during chemotherapy for Burkitt lymphoma or acute lymphoblastic leukemia).

Hypocalcemia also occurs in rhabdomyolysis and in acute severe illnesses (pancreatitis, sepsis, burns).103a,184 In these disorders, the cause of hypocalcemia is unclear, but it may be related to cell lysis with hyperphosphatemia or to movement of calcium into soft tissues with an inadequate acute response of the PTH–vitamin D homeostatic system.