ABSTRACT
Over 99% of body calcium is in bone, of which about 1% is freely exchangeable with extracellular fluid (ECF). Ionised calcium is crucial to many excitatory processes, including nerve and neuromuscular conduction/contraction and coagulation. Normal daily intake is of the order of 10-20mmol and normal total serum calcium is in the range 2.25-2.7mmol l−1. Intestinal calcium absorption is enhanced by 1,25-dihydroxy-vitamin D3 (1,25(OH)2D3). Around 40% is bound to albumin and total serum calcium decreases 0.02mmol l−1 for each 1g l−1 decrease in albumin. Ionised calcium is the physiologically important form and the normal level is 1.15mmol l−1.
