Hypercalcemia is the plasma calcium level above the normal range.
Malignancies may cause hypercalcemia by three different mechanisms (1) excretion of hormone active substances such as PTH-related protein, (2) bone metastases, (3) mulitple myeloma.
Discontinuation of glucocorticoid therapy and Addison syndrome.
Immobilization and long stay in a state of weightlessness.
Sarcoidosis (Boeck) increases the production of Calcitriol.
Milk-alkali syndrome or other types of excessive calcium intake.
Vitamin D overdose.
Vitamin A overdose.
The normal levels of total and ionized calcium are 2.20-2.65mmol/l (8.8-10.6mg/dl) and 1.15-1.35mmol/l (4.6-5.4mg/dl) respectively. The levels in newborns may significantly differ.
The calcium content of an adult 70kg human body is 1,250g (31mol). 99% of total body calcium is located in bone. 99% of bone calcium is incorporated in hydroxyapatite. The remaining 1% belong to an exchangeable pool. 1% of total body calcium is located outside bone tissue, in both intra- and extracellular spaces. Plasma calcium is either ionized, protein bound, or complexed (47.5%, 46.0%, and 6.5%, respectively).
Under normal physiological conditions the daily calcium intake is 1,000mg. 800mg of calcium leave the body by stool. The kidney excretes the remaining 200mg. Daily enteral absorption of calcium is 400mg and concurrent secretion 200mg. Even more calcium is exchanged by the kidney. Circadian filtration is 10,000mg and reabsorption 9,800mg. The bone exchanges 500mg calcium to both directions. The calcium turnover in soft tissues is hardly measurable.
Besides stabilizing bone mineral matrix calcium serves several other physiological functions nerve impulse transmission, muscular contraction, blood coagulation, hormone secretion, and intercellular adhesion.
|Hypophosphatemic rickets with hyperparathyroidism|
The reason for hypercalcemia is rather complex. Elevated PTH levels certainly play a role.