Ionized calcium: analytical challenges and clinical relevance

Abstract

Abstract: Calcium is a central electrolyte involved in many physiological functions commonly measured in clinical practice. Abnormal calcium levels are frequently found, and could have serious clinical consequences. The free form of calcium, also called ionized calcium, plays a determining role in the human body. Its measurement still remains limited by technical, analytical and financial constraints. To overcome these limits, many formulas have been developed to estimate the ionized calcium value. These formulas use blood parameters more easily measurable (total calcium, albumin, and proteins). Although these equations have always been questioned in the scientific literature, their use remains extremely common in clinical practice. Indeed, by their practical aspect, the usefulness of such equations is indisputable in many situations of the clinician daily practice. Conversely, some evidence has more recently pushed to the routine use of the ionized calcium dosage, to the point of potentially switching into a drift of inappropriate over-prescription. The aim of this article is first to describe the application of ionized calcium in clinical practice and to discuss about its measurement and estimation in laboratories.