The per cent of Free or Ionized Calcium in the body is

(C) 50% # IONIZED CALCIUM:> Total calcium consists of free or ionized calcium (50%), calcium bound to protein (40-45%), principally albumin and calcium complexed to anions (5-10%), E.g. citrate, lactate, bicarbonate. Total calcium level does not give an indication of what is available at the cellular level.> Ionized calcium (iCa) is the form of calcium that is readily available to cells, and measurement of iCa is a more accurate reflection of the physiological calcium state.> Measurement of ionized calcium requires instrumentation with ion-specific electrodes. Unlike total calcium, ionized calcium is unaffected by albumin concentration, but it is affected by acid-base balance.> Acidosis (decreased pH) increases iCa, where as Alkalosis (increased pH) decreases iCa.> The pH of blood, serum or plasma changes rapidly with storage (usually decreases with refrigeration and increases with freezing), therefore iCa is unstable in stored blood samples.