SERUM IONIZED MAGNESIUM - RELATION TO BLOOD-PRESSURE AND RACIAL FACTORS

To study potential ionic factors predisposing to vascular disease in h ypertension, particularly among black subjects, we used a recently dev eloped combined magnesium and calcium specific, ion selective electrod e apparatus to measure extracellular ionized calcium (Ca-ion), ionized magnesium (Mg-ion), and Ca-ion/Mg-ion ratios in the serum of fasting, nonmedicated white and black normotensive (n = 61) and hypertensive ( n = 23) subjects, studied consecutively in a tertiary referral center. Both race and blood pressure status had independent effects on the di stribution of Mg-ion values. Although Mg-ion levels for the group as a whole were lower in hypertensive versus in normotensive subjects (0.5 71 +/- 0.012 v 0.601 +/- 0.005 mmol/L; P < .01), this was only true of white subjects (0.579 +/- 0.021 v 0.620 +/- 0.006 mmol/L; P = .0095). The lack of a significant difference in Mg-ion levels between black h ypertensive versus normotensive subjects (0.553 +/- 0.012 v 0.577 +/- 0.007 mmol/L, P = NS) was attributable to the significantly lower Mg-i on levels present in normotensive blacks compared to those in normoten sive white subjects (0.577 +/- 0.007 v 0.620 +/- 0.006 mmol/L, P = .00 01). Resultant Ca-ion/Mg-ion ratios were elevated in all black subject s and in white hypertensive subjects. These data support the presence among hypertensives and among black subjects (independently of blood p ressure) of a consistent depletion of circulating magnesium and of an imbalance of calcium and magnesium that may potentiate vascular diseas e among these subjects. (C) 1997 American Journal of Hypertension, Ltd .