SERUM IONIZED VERSUS TOTAL MAGNESIUM IN PATIENTS WITH CHRONIC RENAL-DISEASE

Background: Recent technology has made it possible to assess serum ion ized magnesium with user-friendly ion-selective electrodes similar to measurement of the serum calcium concentration. Methods: We measured t he serum ionized (Mg2+) and total magnesium (tMg) concentration in 69 patients with chronic kidney disease (38 men, 31 women, age 22-85 year s) and in 75 control subjects. Results: In control subjects the refere nce ranges were as follows: serum Mg2+ 0.45-0.67 mmol/l, and tMg 0.67- 0.96 mmol/l. In patients with chronic renal failure serum Mg2+ was 0.5 7 +/- 0.05 mmol/l and tMg 0.80 +/- 0.11 mmol/l, and in transplant reci pients receiving cyclosporine 0.53 +/- 0.05 and 0.71 +/- 0.10 mmol/l, respectively. The correlation coefficient between serum Mg2+ and tMg w as r = 0.73 (p < 0.001) in the patient group and r = 0.75 (p<0.001) in control subjects. Serum tMg was below the reference range in 15 of 69 measurements. However, serum Mg2+ was below the reference range in on ly I of these 15 samples. Hence, 14 of 69 cases with low tMg but norma l Mg2+ were false-positive with respect to hypomagnesemia. Conclusion: We conclude that tMg may overestimate the incidence of hypomagnesemia , and the measurement of Mg2+ may be of benefit when studying patients with expected hypomagnesemia.