Routine hemodialysis induces a decline in plasma magnesium concentration in most patients: a prospective observational cohort study

In hemodialysis patients, lower plasma magnesium (Mg) concentrations are associated with a higher overall and cardiovascular mortality. The optimal concentration appears to be above the reference range for the healthy population. Plasma Mg is not routinely measured after hemodialysis. Aim of this study was to determine the effect of routine hemodialysis on plasma Mg. Plasma Mg was measured in duplicate before (Mg(pre)) and after (Mg(post)) dialysis in 6 consecutive hemodialysis sessions of 34 patients using a fixed 0.50 mmol/L dialysate Mg concentration. Mean Mg(pre) was 0.88 mmol/L (±0.14) and mean Mg(post) was statistically significantly lower: mean intra-dialytic decline 0.10 mmol/L (95%-CI 0.06–0.13). A 0.10 mmol/L higher Mg(pre) was associated with a 0.03 mmol/L higher Mg(post) (95%-CI 0.024–0.037). At a Mg(pre) of 0.74 mmol/L, Mg(post) equalled Mg(pre). There was an intra-dialytic decline of plasma Mg at higher Mg(pre) values and an increase at lower Mg(pre) values. In conclusion, in the majority of the hemodialysis patients, Mg(pre) concentrations are in the reference range of the healthy population, which may be too low for hemodialysis patients. Routine hemodialysis with the widely used 0.50 mmol/L dialysate Mg concentration, further declines magnesium in the majority of patients. Current dialysate Mg concentrations may be too low.