Measurement of ionized magnesium in whole blood, plasma and serum with a new ion-selective electrode in healthy and diseased human subjects.

A novel ion selective electrode (ISE) for ionized magnesium (IMg2+) in whole blood (WB), plasma (PL), and serum (S) has been designed. We have undertaken a number of studies, experimental and clinical, to characterize and examine the linearity, precision, specificity, accuracy, and utility of this new ISE for IMg2+ in WB, S, and PL of normal human subjects, diseased subjects and animals. Using aqueous solutions, mean IMg2+ values are within 94.6-99.2% of their targets. The linearity of the ISE (0.1-3.0 mM) in aqueous solutions, and human PL and S ranges between 92.0 and 99.3%. The ISE is highly selective for IMg2+, yielding measurements in less than 2 min, and exhibiting no or negligible effects from pathophysiologic concentrations of Ca2+, Na+, K+, H+ or NH4+. Likewise such concentrations of heavy metals (e.g., Fe3+, Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+) in aqueous solution and serum do not interfere with ISE measurements for IMg2+. Ligand binding studies in aqueous solution indicate that pathophysiologic concentrations of different anions (e.g., heparin, bicarbonate, phosphate, acetate, sulfate and lactate) bind to Mg2+ with varying intensities, effectively reducing its concentration in solutions. IMg2+ measurements on WB, PL, and S for a given person's samples are virtually identical. Typically, IMg2+ is 71% of total Mg (TMg) but varies from subject to subject. The IMg2+ is held within a narrow range (0.53-0.67 mM) in normal, healthy controls. Studies on diseased human subjects (i.e., cardiac cases, cardiopulmonary bypass, abnormal pregnancy, renal transplant recipients, diabetics, asthmatics, etc.) indicate that IMg2+ levels often exhibit significant alterations from normality, despite no change in TMg.(ABSTRACT TRUNCATED AT 250 WORDS)