Christopher Holzmann-Littig1, Claudius Kuechle1, Andreas Bietenbeck2, Wendy McCallum3, Uwe Heemann1, Lutz Renders1, Dominik Steubl1. 1. Department of Nephrology, Klinikum rechts der Isar, Faculty of Medicine, Technical University Munich, Munich, Germany. 2. Institute for Clinical Chemistry and Pathobiochemistry, Klinikum rechts der Isar, Faculty of Medicine, Technical University Munich, Munich, Germany. 3. Division of Nephrology, Tufts Medical Center, Boston, Massachusetts, USA.
Abstract
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 (Mgion ) 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 Mgion using linear regression analysis in 191 hemodialysis (HD) patients. Reference test was measured ionized magnesium (Mgion ). As index tests, we chose estimated Mgion using total magnesium (Mgtot ) and other laboratory and demographic variable candidates. Equations were internally validated, using 749 subsequent Mgion measurements. FINDINGS: The median patient age was 65 years, 67.5% of the patients were male. Median (interquartile range [IQR]) measured Mgion 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 Mgtot , serum ionized, and total calcium concentrations. In the validation dataset, bias (i.e., median difference between measured and estimated Mgion , -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: Mgion 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.
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 (Mgion ) 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 Mgion using linear regression analysis in 191 hemodialysis (HD) patients. Reference test was measured ionized magnesium (Mgion ). As index tests, we chose estimated Mgion using total magnesium (Mgtot ) and other laboratory and demographic variable candidates. Equations were internally validated, using 749 subsequent Mgion measurements. FINDINGS: The median patient age was 65 years, 67.5% of the patients were male. Median (interquartile range [IQR]) measured Mgion 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 Mgtot , serum ionized, and total calcium concentrations. In the validation dataset, bias (i.e., median difference between measured and estimated Mgion , -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: Mgion 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.