Estimating serum-ionized magnesium concentration in hemodialysis patients

Introduction: Cardiovascular mortality is significantly increased in kidney failure with replacement therapy (KFRT) patients, which is partly mediated by enhanced vascular calcification. Magnesium appears to have anticalcifying capabilities, and hypomagnesemia has been associated with increased mortality in KFRT patients. Ionized magnesium represents the biologically and physiologically active form. As serum ionized magnesium (Mg_ion) is difficult to assess in clinical routine estimating equations derived from routinely assessed laboratory parameters could facilitate medical treatment. Methods: We developed equations to estimate serum Mg_ion using linear regression analysis in 191 hemodialysis (HD) patients. Reference test was measured ionized magnesium (Mg_ion). As index tests, we chose estimated Mg_ion using total magnesium (Mg_tot) and other laboratory and demographic variable candidates. Equations were internally validated, using 749 subsequent Mg_ion measurements. Findings: The median patient age was 65 years, 67.5% of the patients were male. Median (interquartile range [IQR]) measured Mg_ion was 0.64 [0.57, 0.72] mmol/L, 11 (6%) patients were hypo- (i.e., <0.45 mmol/L) and 127 (66%) were hypermagnesemic (>0.60 mmol/L). The final equation at the end of the development process included Mg_tot, serum ionized, and total calcium concentrations. In the validation dataset, bias (i.e., median difference between measured and estimated Mg_ion, −0.017 [−0.020, −0.014] mmol/L) and precision (i.e., IQR of bias 0.043 [0.039, 0.047] mmol/L) were small, 90% [88, 93] of estimated values were ±10% of measured values. The equation detected normomagnesemia with overall good diagnostic accuracy (area under the receiver-operating curve 0.91 [0.89, 0.93]). Discussion: Mg_ion can be estimated from equations containing routinely assessed laboratory variables with high accuracy and good overall performance. These equations might simplify the assessment of ionized magnesium levels in the individual hemodialysis patients and help the treating physician to guide the overall treatment.