| PTH deficiency |
| Genetic |
| Acquired (e.g., surgical, irradiation, neoplastic invasion) |
| Transient (e.g., hypomagnesemia) |
| Vitamin D deficiency |
| Cholecalciferol deficiency (e.g., sunlight deprivation, dietary insufficiency, gut malabsorption) |
| 25-Hydroxycholecaldferol deficiency (e.g., impaired hepatic hydroxylation, hepatobiliary disease, nephrotic syndrome, anticonvulsant therapy) |
| 1,25-Dihydroxycholecalciferol deficiency (e.g., renal failure, hyperphosphatemia) |
| Transient hypocalcemia |
| Intravascular redistribution (e.g., massive transfusion with acid blood) |
| Sudden increase in net deposition in bone |
| Decreased bone resorption (e.g., mithramycin, calcitonin) |
| Increased mineralization (e.g., treatment of rickets) |
| Increased bone formation (e.g., osteoblastic metastasis) |
| Failure to increase bone resorption in response to calcium depletion (e.g., medullary carcinoma of thyroid) |
| Increased soft tissue deposition (e.g., rhabdomyolysis, pancreatitis, hyperphosphatemia) |
Source: Modified from Parfitt and Kleerekoper, 1980.
From: Chapter 143, Serum Calcium
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