half in a relatively stable, nondiffusable, protein-bound form; a very small percent in a labile, diffusable, complex form bound to other substances in the plasma and interstitial fluids; and the rest in an ionized form(2). Only when calcium is ionized, is it effective in physiological mechanisms. But there is a dynamic relationship among all three forms of calcium, with a constant shifting from one form to another to maintain serum calcium levels within the normal