The normal range for total serum calcium is 8.5-10.5 mg/dL or 4.5-5.5 mEq/L. Ninety-nine percent of calcium is located in the bones and teeth and is responsible for the formation and firm structure of these body parts. This leaves 1% of calcium in the cells and fluid compartments, with the majority of that 1% in the extracellular compartment. Forty-one percent of this extracellular calcium is bound to the protein albumin. Therefore when albumin levels decline, so do calcium levels. A small percentage is bound to citrate and other small organic ions. The remainder of calcium is ionized (unbound). The
normal value for ionized calcium is 4.5-5.1 mg/dL or 2.2-2.5 mEq/L. This ionized or free calcium conducts the physiological functions, and any imbalances in the levels of ionized calcium result in hypocalcemia or hypercalcemia. Calcium functions in cellular permeability and in the contraction of cardiac, smooth, and skeletal muscles. It also plays a role in the blood-clotting process.