Reference values for ionized, complexed, and protein-bound plasma magnesium in men and women.

Of the three magnesium fractions in plasma, free ionized magnesium (Mg2+) has the greatest biological activity. Accordingly, information concerning this form in plasma is of cardinal importance to investigations in biometry and human pathology. For this reason, we developed an indirect assay for ionized magnesium in which Mg2+ is determined as the difference between ultrafiltrable magnesium, as measured in plasma water after ultracentrifugation, and complexed magnesium, as obtained after fixation of the ionized and protein-bound magnesium on Amberlite IR-120(H) cation-exchange resin. All magnesium assays were performed by atomic absorption spectrometry. We used this methodology to compare ionized, complexed, and protein-bound plasma magnesium in 34 normal men and 12 normal women. Sex-related differences between the values for these fractions were not significant. Interesting preliminary results for cases of myocardial infarction prompt us to continue our investigations concerning these three states of plasma magnesium in cardiac pathology.