MO649: Monitoring of Ionized Magnesium in Haemodialysis Patients: A Useful Tool to Allow a Personalized Prescription of Dialysate Composition

Abstract

Abstract BACKGROUND AND AIMS In healthy subjects, normal values of magnesium (Mg) are in the range 0.75–0.95 mmol/L. In the circulation, 65–70% of the Mg is present in the free, ionized and dialyzable form (i.e. 0.45– 0.60 mmol/L), 20% is bound to proteins and 15% is complexed. In chronic kidney disease (CKD) dialysis patients, the dialysate Mg concentration is a major determinant of Mg balance. The aim of this study was to assess the systemic variations of ionized Mg (iMg), as well as that of ionized calcium (iCa), before and after a dialysis session. METHOD A total of 121 dialysis patients [median age = 70 (62.5–78.2) years; 74 male/46 female] in maintenance haemodialysis three times per week, for at least 6 months and with no residual function, were included. Patients were assigned to a single dialysis session with either control fluid (group 1: 3 mM acetate, 1.5 mM Ca, 0.5 mM Mg), or citrate dialysis fluid containing 0.5 mM Mg (group 2: 0.8 mM citrate, 0.3 mM acetate, 1.65 mM Ca) or 0.75 mM Mg (group 3: 0.8 mM citrate, 0.3 mM acetate, 1.65 mM Ca). Blood samples were drawn before and after the midweek dialysis sessions as part of the routine patient follow-up and quality assurance process. iMg and iCa concentrations were measured by direct ion-selective electrode on Nova Stat Profile Prime Plus® (Nova Biomedical). Total Mg (tMg) and Ca (tCa) were assessed by colorimetric method c702/Cobas 8000 analyzer (Roche). Dialytic balance was assessed by the median intra-dialytic difference between pre-dialysis and post-dialysis. RESULTS The use of all types of dialysates (whatever their composition was) was associated with a calcium load during the session (Table). In addition, an Mg loss was observed in both control and citrate dialysis fluid groups containing 0.5 mM Mg. The dialysis session induced a significant decrease in iMg (13 and 22% in group1 and group 2 respectively). By contrast, the use of citrate dialysis fluid with 0.75 mM Mg led to a positive balance with a median intra-dialytic increase of 0.08 and 0.02 mmol/L in tMg and iMg respectively (Table), corresponding to a median increase of 8 and 3% in tMg and iMg respectively. CONCLUSION The iMg fraction represents 70% of tMg in CKD stage 5D patients. While a dialysate Mg concentration at 0.5 mM leads to a negative balance, increasing the concentration to 0.75 mM significantly raises post-dialysis circulating Mg levels in these patients. Therefore, monitoring of iMg should allow a personalized prescription in dialysate Mg composition.