Importance of Ionized Magnesium Measurements in Physiology and Medicine and the Need for Ion-selective Electrodes

Mg is a co-factor for more than 500 enzyme systems, and is the second most abundant intracellular cation after potassium. It is critical in numerous physiological, cellular and biochemical functions and systems, running the gamut from hormone-receptor binding, transmembrane fluxes of cations and anions, muscle contraction, nerve conduction, cardiac functions and stability, control of vasomotor tone and distribution of blood flows, among many others. Serum total Mg measurements have suggested that it is depleted in numerous types of hospitalized patients. Mg is depleted in normal methods of food preparation (e.g., boiling, frying, etc.) and processing. The daily intake of Mg has been declining since 1900, from where it was about 500-600 mg/day to 150-225 mg/ day. Surprisingly, most mammals, including humans, exhibit similar levels of serum Mg. Overall, this has suggested that total Mg measurements on serum or plasma aren't sensitive blood variables or analytes to reflect what may be going on at the cellular and subcellular levels. Moreover, Mg is known to exist in at least three forms: free or ionized, complexed, and protein-bound. In addition, up until our studies, there were no methods to measure ionized Mg on whole blood specimens needed for rapid analysis in the ER and OR. In this report, we review many of the strides that have been made in utilization of Mg2+ ion-selective electrodes, their accuracy, and their uses in numerous human diseases, pathophysiological states, and in animals. It is our contention that the use of Mg2+ ion-selective electrodes should prove invaluable in the diagnosis and treatment of numerous diseases. These ISEs should also be very useful, clinically, in determining Mg body homeostasis and whether dietary intakes of Mg are providing enough Mg.