Disorders of calcium metabolism

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The serum level of calcium is closely regulated within a fairly limited range in the human body, with a normal total calcium of 2.2-2.6 mmol/L (9-10.5 mg/dl), and a normal ionized calcium of 1.1-1.4 mmol/L (4.5-5.6 mg/dL). The amount of biologically active calcium varies with the level of 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 total calcium of less than 4.0 mg/dL is considered hypocalcemia, while a total calcium of more than 11.0 mg/dL is considered hypercalcemia.

Table of contents

1 Hypocalcemia

1.1 Causes

2 Hypercalcemia

2.2 Symptoms
2.3 Causes
2.4 Treatments:

Hypocalcemia

Causes

absent parathyroid hormone (PTH)
- hereditary hypoparathyroidism
- acquired hypoparathyroidism
- hypomagnesemia
ineffective PTH
- chronic renal failure
- absent active vitamin D
  - decreased dietary intake
  - decreased sun exposure
  - defective Vitamin D metabolism
    - anticonvulsant therapy
    - vitamin-D dependent rickets, type I
- ineffective active vitamin D
  - intestinal malabsorption
  - vitamin-D dependent rickets, type II
- pseudohypoparathyroidism
deficient PTH
- severe acute hypophosphatemia
  - tumor lysis syndrome
  - acute renal failure
  - rhabdomyolysis
- osteitis fibrosa following parathyroidectomy

Hypercalcemia

Symptoms

Hypercalcemia can be an asymptomatic laboratory finding, but because an elevated calcium level is often a clue to other serious disease, a diagnosis should be undertaken if it persists. Hypercalcemia per se can result in fatigue, depression, confusion, anorexia, nausea, vomiting, constipation, or increased urination; if it is chronic it can result in urinary calculi (renal stones or bladder stones). Abnormal heart rhythms can result, and an EKG finding of a short QT interval suggests hypercalcemia. Symptoms are more commin at high calcium levels (11.5-12.0 mg/dL). Severe hypercalcemia (15 mg/dL or more) is considered a medical emergency: at these levels, coma and cardiac arrest can result.

Causes

abnormal parathyroid gland function
- primary hyperparthyroidism
  - solitary adenomas
  - multiple endocrine neoplasia (MEN)
- lithium use
- familial hypocalciuric hypercalcemia
malignancy
- solid tumor with metastasis (e.g. breast cancer)
- solid tumor with humoral mediation of hypercalcemia (e.g. lung or kidney cancer)
- hematologic malignancy (multiple myeloma, lymphoma, leukemia
vitamin-D metabolic disorders
- hypervitaminosis D (vitamin D intoxication)
- elevated 1,25(OH)₂D levels (e.g. sarcoidosis and other granulomatous diseases)
- idiopathic hypercalcemia of infancy
disorders related to high bone-turnover rates
- hyperthyroidism
- prolonged immobilization
- thiazide use
- vitamin A intoxication
renal failure
- severe secondary hyperparathyroidism
- aluminum intoxication
- milk-alkali syndrome]

Treatments:

Definitive treatment is directed at the underlying cause. Emergency treatment consists of intravenous hydration, increased salt intake, use of diuretics, and in extreme cases such drugs as biphosphonates or calcitonin.