Hypocalcemia

Hypocalcemia is plasma calcium below the normal range, often accompanied by cramps.

Physiology

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.

Diseases

Hypomagnesemia with hypercalciuria and nephrocalcinosis with ocular involvement
	Hypocalcemia is typical of FHHNC with ocular involvement though hypomagnesemia is essential. Other crucial symptoms are nephrocalcinosis, recurrent kidney stones, progressive renal failure, and macular coloboma.
Hypomagnesemia with hypercalciuria and nephrocalcinosis
	Hypocalcemia is typical of FHHNC without ocular involvement though hypomagnesemia is essential. Other crucial symptoms are nephrocalcinosis, recurrent kidney stones, and progressive renal failure.

References:

1.	Moe OW et al. (2005) Genetic hypercalciuria.