Free Magnesium in Patients on Regular Dialysis Treatment

Field: Medicine (Health Sciences)

Dear Sir,In end-stage renal disease (ERSD) some severe changes in human homeostasis appear. This is well manifested in electrolyte balance. Calcium and Phosphates are often tested, but studies show significant disorders in magnesium homeostasis too. Magnesium metabolism in man is very important. Magnesium is a biological antagonist of calcium in the human body [1]. It stimulates many enzyme systems [2], influences nervous-muscular excitement [3], affects lipid status [4]and suppresses the release of parathyroid hormone from parathyroid glands [3].The normal total plasma magnesium amount is 1% of total magnesium in the human body. It comprises approximately 60% free magnesium (Mg2+), 20% protein bound, and 5–10% complexed to HCO–3, PO43–, and citrate [5]. Total plasma magnesium is a usual objective in research. In ESRD there is hypermagnesemia conditioned by a disturbance in renal function and increased tissue catabolism [6, 7].The object of this study was to analyze the free magnesium level in patients on regular dialysis treatment (RDT). We tested 64 patients (39 women and 25 men, mean age 49.3 ± 12.7 years, and mean duration of hemodialysis 54.5 ± 14.1 months) treated with bicarbonate hemodialysis thrice weekly for 4 h with a magnesium concentration of 0.51 mmol/l in the dialysate. A control group of healthy adults was also tested.We studied free magnesium (determined by an ion-selective electrode) and total serum magnesium. We also tested hemoglobin, hematocrit, red blood cell count, white blood cell count, urea, creatinine, total serum protein, serum albumin, prealbumin, alkaline phosphatase, total serum calcium, ionized calcium, phosphates, and parathyroid hormone (PTH).In the study of total plasma magnesium we observed higher than normal levels in 19 patients (30%) before hemodialysis. Total serum magnesium decreased to normal after hemodialysis. The mean free magnesium level in the healthy adults of the control group was 0.444 ± 0.074 mmol/l.By studying the free magnesium level in patients on RDT we found hypermagnesemia in all of them (100%) before (0.688 ± 0.097 mmol/l) and after the hemodialysis (0.610 ± 0.090 mmol/l). The reduction in free magnesium after hemodialysis was significant (p < 0.01). There were no significant differences between men and women.The correlation of free magnesium with other indexes is presented in table 1. The results showed that the correlation between free magnesium and calcium and phosphates was lower than expected, probably due to the calcium supplements and phosphate binders used. The negative correlation between free magnesium and PTH is most pronounced. It supports the suggestion that hypermagnesemia suppresses the release of PTH from parathyroid glands.While increased total serum magnesium was registered in 30% of the hemodialysis patients, free magnesium was increased in 100% of them, which shows the biological significance of free magnesium disturbances.Our study confirms that free magnesium is an important parameter in patients on RDT. The results suggest severe disturbances in magnesium homeostasis in hemodialysis patients. The decrease in free magnesium at the end of hemodialysis (from 0.688 ± 0.097 to 0.610 ± 0.090 mmol/l) was due to the lower magnesium content of the dialysate.