In meicine, hypocalcemia is the presence of low serum calcium levels in the blood, usually taken as less than 2.1 mmol/L or 9 mg/dl or an ionized calcium level of less than 1.1 mmol/L (4.5 mg/dL). It is a type of electrolyte disturbance. In the blood, about half of all calcium is bound to proteins such as serum albumin, but it is the unbound, or ionized, calcium that the body regulates. If a person has abnormal levels of blood proteins, then the plasma calcium may be inaccurate. The ionized calcium level is considered more clinically accurate in this case.