#879 Impacts on ionized magnesium and total magnesium by the conversion to higher dialysate magnesium concentration
Authors: Ito Katsuaki , Seo Akihiko , Uchida Hideaki , Shinjo Hitomi , Suwata Junji 
Published: May 2024

Abstract

Background and Aims
Hypermagnesemia is detrimental to hemodialysis patients whose renal function is compromised. However, recent observational study suggested the lower mortality rate was observed in the patients with mild hypermagnesemia. Even though the serum magnesium concentration (tMg) of the patients were frequently higher than the reference range of the tMg, one study reported 90% of the cases were within the reference range of the ionized magnesium (iMg) which is a physiologically active fraction of magnesium (Mg) in the blood. This is due to the higher serum phosphorous level in the hemodialysis patients, and negative correlation between iMg and the serum phosphorous, and anion gap.
Current guideline recommends Mg level should be managed to be 3.0 mg/dL at pre-dialysis blood test. However, not much are known what iMg level is optimal. This study aimed to assess the impacts on iMg and tMg level of the patients by the conversion of the routinely-used dialysate containing 1.0 mEq/L (0.5 mmol/L) Mg to higher dialysate Mg concentration.

Method
This longitudinal study was conducted at Shingashi Renal Centre, Fujimino Renal Centre, and Kawagoe-minami Renal Centre. Out of 289 stable maintenance hemodialysis patients agreed to participate in the study, 42 were excluded due to death, changing hospital, or hospitalization. A total of 247 patients who are on regular hemodialysis treatment at least 6 months with commercially available dialysate mixture TA1 (Mg concentration: 1.0 mEq/L (0.5 mmol/L)) were included for the analysis. Dialysate Mg concentration was then increased to 1.25 mEq/L (0.625 mmol/L) by using a commercially available dialysate mixture TA5. Blood tests were carried out on the day of the first hemodialysis session of the week (Monday or Tuesday) before dialysate Mg concentration conversion and at 1, 4, 12, and 24 weeks.
The iMg concentrations were analyzed using the ion-selective electrode on blood gas analyzer StatProfile Prime Plus (Nova Biomedical, Waltham, MA, USA). The tMg concentrations were determined by using Xylidylblue.

Results
Mean age of the 247 enrolled patients was 70.3ion-selective electrode on blood gas analyzer StatProfile Prime Plus (Nova Bidecreased significantly (TA1-pre:2.58±0.36mg/dL→TA1-post:2.18±0.16mg/dL, TA5-pre (24wk): 2.74±0.35mg/dL→TA5-post: 2.44±0.15mg/dL). After conversion to higher Mg dialysate TA5, post-dialysis tMg increased in comparison with TA1. After conversion to the higher Mg dialysate, iMg increased as well significantly (TA1-pre:0.64±0.11mmol/L→TA1-post:0.49±0.05mmol/L, TA5-pre:0.70±0.11mmol/L→0.60±0.04mmol/L) . However, iMg of TA1-post was close to the lower limit of the reference range of iMg (Fig. 1).

Conclusion
Hemodialysis patients’ iMg level became manageable within reference range by the conversion of the dialysate from TA1 to TA5 and the clinical advantage of iMg monitoring with hemodialysis patients were demonstrated. A slight increase in dialysate Mg concentration from 1.0 mEq/L to 1.25 mEq/L increased the iMg/tMg ratio, and iMg was within the normal range even when the pre-dialysis reference value of 3 mg/dL was not reached.