ABSTRACT

Ninety nine per cent of body calcium is skeletal. Plasma calcium exists in several states; a non-diffusible, protein or albumin bound fraction (40%), an ionised or free calcium element (approximately 50%), and the remaining 10% complexed to anions such as bicarbonate and phosphate. The protein-bound fraction is of little physiological significance. Total plasma calcium assays are corrected to account for variations and abnormalities in plasma albumin concentration. Automated biochemical analysis usually measures total plasma calcium. The normal range is from 2.20 to 2.70 mmol. Venepuncture performed with a tourniquet, with the patient standing, or following a meal, may all increase the measured concentration of plasma calcium.