Low PTH (hypoparathyroidism) |
Genetic disorders |
Abnormal parathyroid gland development |
Abnormal PTH synthesis |
Activating mutations of calcium-sensing receptor (autosomal dominant hypocalcemia or sporadic isolated hypoparathyroidism) |
Postsurgical (thyroidectomy, parathyroidectomy, radical neck dissection) |
Autoimmune |
Autoimmune polyglandular syndrome (associated with chronic mucocutaneous candidiasis and primary adrenal insufficiency) |
Isolated hypoparathyroidism due to activating antibodies to calcium-sensing receptor |
Infiltration of the parathyroid gland (granulomatous, iron overload, metastases) |
Radiation-induced destruction parathyroid glands |
Hungry bone syndrome (post-parathyroidectomy) |
HIV infection |
High PTH (secondary hyperparathyroidism in response to hypocalcemia) |
Vitamin D deficiency or resistance |
Multiple causes |
PTH resistance |
Missense mutation in PTH |
Pseudohypoparathyroidism |
Hypomagnesemia |
Kidney disease |
Loss of calcium from the circulation |
Hyperphosphatemia |
Tumor lysis |
Acute pancreatitis |
Osteoblastic metastases |
Acute respiratory alkalosis |
Sepsis or acute severe illness |
Drugs |
Inhibitors of bone resorption (bisphosphonates, calcitonin, denosumab), especially in vitamin D deficiency |
Cinacalcet |
Calcium chelators (EDTA, citrate, phosphate) |
Foscarnet (due to intravascular complexing with calcium) |
Selected gadolinium-based contrast agents (gadodiamide, gadoversetamide) may cause spurious hypocalcemia by interfering with laboratory measurement of total calcium |
Phenytoin (due to conversion of vitamin D to inactive metabolites) |
Fluoride poisoning |
Disorders of magnesium metabolism |
Hypomagnesemia can reduce PTH secretion or cause PTH resistance and is therefore associated with normal, low, or high PTH levels |
Data from: Thakker RV. Hypocalcemia: Pathogenesis, differential diagnosis, and management. In: Primer on the metabolic bone diseases and disorders of mineral metabolism, sixth edition, American Society of Bone and Mineral Research 2006; 35:213.
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