Hypocalcemia is a condition that Serum calcium less than 2.2mmol / L. Normal serum calcium concentration remained stable for 2.25 ~ 2.75 mmol / L, children higher. Plasma and body fluids in the combination of calcium mainly calcium and free calcium exist in two ways. Major calcium binding protein binding and clearance, and a small amount of organic acids with calcium such as arrests Hengchuan, calcium lactate, calcium phosphate and so on. Free calcium and the combination of a continuous exchange of calcium in a dynamic equilibrium, which is mainly affected by the effects of pH. Acidosis when the free calcium (Ca2 +) increase in alkalosis when combined with an increase in calcium. In addition between the concentration of calcium and phosphorus to maintain a certain product, that is, [Ca] × [P] = 350-400 mg / L. Free calcium was only really with the physiological function of calcium.