Hypocalcemia varies from an asymptomatic biochemical abnormality to a life-threatening disorder, depending on the duration, severity, and rapidity of development. Hypocalcemia is caused by loss of calcium from or insufficient entry of calcium into the circulation.

Hypoparathyroidism is the most common cause of hypocalcemia and often develops because of surgery in the central neck requiring radical resection of head and neck cancers. It develops in 1% to 2% of patients after total thyroidectomy.

The hypocalcemia may be transient, permanent, or intermittent, as with vitamin D deficiency during the winter. Autoimmune hypoparathyroidism is seen as an isolated defect or as part of polyglandular autoimmune syndrome type I in association with adrenal insufficiency and mucocutaneous candidiasis. Most of these patients have autoantibodies directed against the calcium-sensing receptor. Congenital causes of hypocalcemia include activating mutations of calcium-sensing receptor, which has reset the calcium–parathyroid hormone (PTH) relation to a lower serum calcium level. Mutations affecting intracellular processing of the pre-pro-PTH molecule are also described and lead to hypoparathyroidism, hypocalcemia, or both. Finally, some cases are associated with hypoplasia or aplasia of the parathyroid glands; the best known is DiGeorge syndrome.

Pseudohypoparathyroidism is a group of disorders with postreceptor resistance to PTH. One classic variant is Albright’s hereditary osteodystrophy, associated with low stature, round facies, short digits, and mental retardation. Hypomagnesemia induces PTH resistance and also affects PTH production. Severe hypermagnesemia (>6 mg/dL) can lead to hypocalcemia by inhibiting PTH secretion. Vitamin D deficiency leads to hypocalcemia when associated with decreased dietary calcium intake. The low calcium level stimulates PTH secretion (secondary hyperparathyroidism), leading to hypophosphatemia.

Rhabdomyolysis and tumor lysis syndrome cause loss of calcium from the circulation when large amounts of intracellular phos-phate are released and precipitate calcium in bone and extraskeletal tissues. A similar mechanism causes hypocalcemia with phosphate administration.

Acute pancreatitis precipitates calcium as a soap in the abdomen, causing hypocalcemia. Hungry bone syndrome is hypocalcemia after surgery for hyperparathyroidism (HPT) in patients with severe prolonged disease (secondary or tertiary HPT in renal failure). Serum calcium is rapidly deposited into the bone. Hungry bone syndrome is rarely seen after correction of longstanding metabolic acidosis or after thyroidectomy for hyperthyroidism.

Several medications (e.g., ethylenediaminetetraacetic acid [EDTA], citrate present in transfused blood, lactate, foscarnet) chelate calcium in the circulation, sometimes producing hypocalcemia in which ionized calcium is decreased, cohereas total calcium may be normal. Extensive osteoblastic skeletal metastases (prostate and breast cancers) may also cause hypocalcemia. Chemotherapy, including cisplatin, 5-fluorouracil, and leucovorin, causes hypocalcemia mediated through hypomagnesemia. Hypocalcemia after surgery can be mediated by the citrate content of transfused blood or by a large volume of fluid administration and hypoalbuminemia. Patients with sepsis demonstrate hypocalcemia usually associated with hypoalbuminemia.

Ionized means charged. Sepsis is the other cause of hypocalcemia (absence of PTH secretion or hypoparathyroidism). Low calcium, high magnesium and low Vitamin D3. Can also be congenital (mutations of CaSR, PTH, and parathyroid aplasia)

Supplementation of calcium 60%, magnesium 40% with zinc, Vitamin D and C and should be taken before eating food rich in iron since iron cancels calcium absorption.