Table 2. Causes of hypocalcemia.

PTH: parathyroid hormone; CKD: chronic kidney disease

Causes

PTH deficiency: hereditary (e.g., isolated congenital hypoparathyroidism, DiGeorge syndrome) or acquired hypoparathyroidism, post-parathyroidectomy and post-thyroidectomy, post-parathyroid glands radiation

Vitamin D deficiency or resistance [lack of sun exposure, inadequate dietary intake, intestinal malabsorption (steatorrhea), hepatic disease, CKD, osteomalacia, rickets]

Increased Ca+2 uptake as in rhabdomyolysis, tumor lysis syndrome, hungry bone syndrome (post-parathyroidectomy), or acute pancreatitis

Ca+2 malabsorption due to small bowel pathologies such as short bowel syndrome and sprue

Acute hyperventilation (which results in respiratory alkalosis)

Low dietary intake of Ca+2 (rare in the absence of intestinal malabsorption or vitamin D deficiency)

Osteoclastic bone metastases as in prostate cancer and small cell lung cancer

Pseudohypoparathyroidism, which is a rare genetic disorder characterized by resistance to PTH actions

Hypermagnesemia and profound hypomagnesemia (due to suppression of PTH secretion)

Acute severe hyperphosphatemia

Intake of Ca+2-binding ingredients such as oxalate, phosphate, and cellulose

Medications: bisphosphonate, denosumab, cinacalcet, etelcalcetide

Massive blood transfusion due to binding of ionized Ca+2 with citrate

Critical illness

Pseudohypocalcemia caused by some gadolinium contrast agents (e.g., gadoversetamide) due to interference with total calcium laboratory assay