Disorders of calcium metabolism

Hypocalcemia is common and can occur unnoticed with no symptoms or, in severe cases, can have dramatic symptoms and be life-threatening.[1] Hypocalcemia can be parathyroid related or vitamin D related. Parathyroid related hypocalcemia includes post-surgical hypoparathyroidism, inherited hypoparathyroidism, pseudohypoparathyroidism, and pseudo-pseudohypoparathyroidism.[1] Post-surgical hypoparathyroidism is the most common form, and can be temporary (due to suppression of tissue after removal of a malfunctioning gland) or permanent, if all parathyroid tissue has been removed.[1] Inherited hypoparathyroidism is rare and is due to a mutation in the calcium sensing receptor. Pseudohypoparathyroidism is maternally inherited and is categorized by hypocalcemia and hyperphosphatemia. Finally, pseudo-pseudohypoparathyroidism is paternally inherited. Patients display normal parathyroid hormone action in the kidney, but exhibit altered parathyroid hormone action in the bone.[1] Vitamin D related hypocalcemia may be associated with a lack of vitamin D in the diet, a lack of sufficient UV exposure, or disturbances in renal function. Low vitamin D in the body can lead to a lack of calcium absorption and secondary hyperparathyroidism (hypocalcemia and raised parathyroid hormone).[1] Symptoms of hypocalcemia include numbness in fingers and toes, muscle cramps, irritability, impaired mental capacity and muscle twitching.[1]

Hypercalcemia is suspected to occur in approximately 1 in 500 adults in the general adult population.[2] Like hypocalcemia, hypercalcemia can be non-severe and present with no symptoms, or it may be severe, with life-threatening symptoms. Hypercalcemia is most commonly caused by hyperparathyroidism and by malignancy, and less commonly by vitamin D intoxication, familial hypocalciuric hypercalcemia and by sarcoidosis.[2] Hyperparathyroidism occurs most commonly in postmenopausal women. Hyperparathyroidism can be caused by a tumor, or adenoma, in the parathyroid gland or by increased levels of parathyroid hormone due to hypocalcemia.[2] Approximately 10% of individuals with cancer experience hypercalcemia due to malignancy.[2] Hypercalcemia occurs most commonly in breast cancer, lymphoma, prostate cancer, thyroid cancer, lung cancer, myeloma, and colon cancer.[2] It may be caused by secretion of parathyroid hormone-related peptide by the tumor (which has the same action as parathyroid hormone), or may be a result of direct invasion of the bone, causing calcium release.[2] Symptoms of hypercalcemia include anorexia, nausea, vomiting, constipation, abdominal pain, lethargy, depression, confusion, polyuria, polydipsia and generalized aches and pains.[2]

The amount of biologically active calcium varies with the level of serum albumin, a protein to which calcium is bound, and therefore levels of ionized calcium are better measures than a total calcium; however, one can correct a total calcium if the albumin level is known.

• A normal ionized calcium is 1.12-1.45 mmol/L (4.54-5.61 mg/dL).
• A normal total calcium is 2.2-2.6 mmol/L (9-10.5 mg/dl).
  • Total calcium of less than 8.0 mg/dL is hypocalcaemia, with levels below 1.59 mmol/L (6 mg/dL) generally fatal.
  • Total calcium of more than 10.6 mg/dL is hypercalcaemia, with levels over 3.753 mmol/L (15.12 mg/dL) generally fatal.

• Calcium metabolism
• Milk-alkali syndrome