Ionized and total serum magnesium in hemodialysis: predictors and variability. A longitudinal cross-sectional study

Ionized and total magnesium levels in patients with chronic kidney disease: associated factors and outcomes

Background

The association between hypo- and/or hypermagnesaemia and cardiovascular (CV) outcomes or mortality has shown conflicting results in chronic kidney disease (CKD) and has been conducted on total magnesium (tMg) levels. Thus, the objectives of the present study were to (i) describe the serum ionized Mg (iMg) concentration in patients at various CKD stages, (ii) measure the correlation between iMg and tMg concentrations, (iii) identify their associated factors and (iv) determine whether serum tMg and/or iMg concentrations are associated with major adverse cardiovascular events (MACE) and mortality before kidney replacement therapy in CKD patients.

Methods

Chronic Kidney Disease-Renal Epidemiology and Information Network (CKD-REIN) is a prospective cohort of CKD patients with an estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m2. Baseline iMg and tMg serum concentrations were centrally measured. Adjusted cause-specific Cox proportional hazard models were used to estimate hazard ratios (HRs) for first MACE and for mortality.

Results

Of the 2419 included patients, median age was 68 years, and the mean eGFR was 34.8 mL/min/1.73 m2. Concentrations of serum iMg and tMg were strongly correlated (r = 0.89, P < .001) and were independently associated with eGFR. The adjusted HR [95% confidence interval (CI)] for MACE associated with the baseline serum tMg level was 1.27 (0.95; 1.69) for patients in Tertile 1 and 1.56 (1.18; 2.06) for patients in Tertile 3, relative to patients in Tertile 2. The HR (95% CI) of death according to serum tMg concentration was increased in Tertile 3 [1.48 (1.11; 1.97)]. The adjusted risk for MACE and mortality (all-cause or CV) associated with the baseline serum iMg level was not significantly different between tertiles.

Conclusions

Our analysis of a large cohort of patients with moderate-to-advanced CKD demonstrated that individuals with higher serum tMg concentrations, although still within the normal range, had a greater likelihood of MACE and mortality. However, serum iMg levels were not associated with these outcomes.

Two Cases of Liver Transplantation With a High Ionized Magnesium to Total Magnesium Ratio

Magnesium (Mg), an important cation, is involved in the activation of enzymes important for life support. The incidence of hypomagnesemia in critically ill patients admitted to the intensive care unit (ICU) is high and has been reported to be a factor in worsening prognosis. Ionized magnesium (iMg) is physiologically active, although total magnesium (tMg) is often used to evaluate the concentration of magnesium because of the limited availability of instruments that can measure iMg. However, the changes in tMg and iMg are not correlated in critically ill patients. We obtained considerable data on the simultaneous measurements of iMg and tMg in two patients with severe liver disease who underwent liver transplantation. In both patients, the iMg/tMg values were high, suggesting the influence of hypoalbuminemia associated with liver dysfunction. Mg correction using tMg as a guide may lead to overdose. Furthermore, when considering the data for each case, the correlation between iMg and tMg was very high, which suggested that the iMg/tMg ratio may be a value unique to each individual or disease. Investigating in a large-scale study the correlation between iMg levels and clinical symptoms and prognosis is necessary in the future.

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.

Successful Management of Refractory Torsades De Pointes Due to Drug-Induced Long QT Syndrome Guided by Point-of-Care Monitoring of Ionized Magnesium

Ionized magnesium (iMg) is the physiologically active fraction, although total magnesium (tMg) is often used clinically because a dedicated electrode is required to measure the iMg concentration. The tMg concentration is not correlated with the iMg concentration, especially in severely ill patients. In this report, a case of refractory torsades de pointes (TdP) due to drug-induced long QT syndrome was successfully treated with high-dose magnesium sulfate guided by point-of-care monitoring of the iMg concentration. A woman in her 60s had taken osimertinib for two months to treat lung cancer. TdP occurred after the operation of a thoracic compression fracture under general anesthesia. She was diagnosed with drug-induced long QT syndrome. TdP continued, despite treatment with 6 g magnesium sulfate. The iMg value on the admission to the intensive care unit was 0.92 mmol/L, but TdP occurred intermittently and circulatory dynamics were unstable. After an additional intravenous administration of 1 g magnesium sulfate, continuous intravenous administration was initiated at 1 g/h. TdP terminated when the iMg concentration reached 1.31 mmol/L. Then, the target iMg was set to 1.3 mmol/L. The iMg concentration was measured every two hours to adjust the continuous dose of magnesium sulfate. Magnesium administration was tapered, and she was transferred to a general ward on the third day. She was discharged without complications on the 11th day. Point-of-care monitoring of the iMg concentration and observation of the patient's clinical symptoms were important for the effective and safe treatment of TdP due to drug-induced long QT syndrome.

Consequences of Supraphysiological Dialysate Magnesium on Arterial Stiffness, Hemodynamic Profile, and Endothelial Function in Hemodialysis: A Randomized Crossover Study Followed by a Non-Controlled Follow-Up Phase

Introduction

Increasing dialysate magnesium (D-Mg²⁺) appears to be an intriguing strategy to obtain cardiovascular benefits in subjects with end-stage kidney disease (ESKD) on hemodialysis. To date, however, hemodialysis guidelines do not suggest to increase D-Mg²⁺ routinely set at 0.50 mmol/L.

Methods

A randomized 4-week crossover study aimed at investigating the consequences of increasing D-Mg²⁺ from 0.50 to 0.75 mmol/L on arterial stiffness, hemodynamic profile, and endothelial function in subjects undergoing hemodialysis. The long-term effect of higher D-Mg²⁺ on mineral metabolism markers was investigated in a 6-month follow-up. Data were analyzed by linear mixed models for repeated measures.

Results

Data of 39 patients were analyzed. Pulse wave velocity and pulse pressure significantly decreased on the higher D-Mg²⁺ compared with the standard one by − 0.91 m/s (95% confidence interval − 1.52 to − 0.29; p = 0.01) and − 9.61 mmHg (− 18.89 to − 0.33, p = 0.04), respectively. A significant reduction in systolic blood pressure of − 12.96 mmHg (− 24.71 to − 1.22, p = 0.03) was also observed. No period or carryover effects were observed. During the long-term follow-up phase the higher D-Mg²⁺ significantly increased ionized and total serum Mg (respectively from 0.54 to 0.64 and from 0.84 to 1.07 mmol/L; mean percentage change from baseline to follow-up + 21% and + 27%; p ≤ 0.001), while parathormone (PTH) decreased significantly (from 36.6 to 34.4 pmol/L; % change − 11%, p = 0.03).

Conclusions

Increasing dialysate magnesium improves vascular stiffness in subjects undergoing maintenance hemodialysis. The present findings merit a larger trial to evaluate the effects of 0.75 mmol/L D-Mg²⁺ on major clinical outcomes.

Trial Registration

The study was retrospectively registered on the ISRCTN registry (ISRCTN 74139255) on 18 June 2020.

Serum magnesium, bone-mineral metabolism markers and their interactions with kidney function on subsequent risk of peripheral artery disease: the Atherosclerosis Risk in Communities Study

BACKGROUND

Few studies have investigated the association of magnesium levels with incident peripheral artery disease (PAD) despite emerging evidence of magnesium contributing to vascular calcification. Moreover, no data are available on whether the magnesium-PAD relationship is independent of or modified by kidney function.

METHODS

A cohort of 11 839 participants free of PAD in the Atherosclerosis Risk in Communities Study at Visit 2 (1990-92) was studied. We investigated the association of serum magnesium and other bone-mineral metabolism markers [calcium, phosphorus, intact parathyroid hormone (iPTH) and intact fibroblast growth factor-23] with incident PAD using multivariable Cox proportional hazards regression.

RESULTS

Over a median of 23 years, there were 471 cases of incident PAD. The hazard ratio for incident PAD in Quartile 1 (<1.5 mEq/L) versus Quartile 4 (>1.7 mEq/L) of magnesium was 1.96 (95% confidence interval 1.40-2.74) after adjustment for potential confounders. Lower magnesium levels were associated with greater incidence of PAD, particularly in those with estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m2 (n = 11 606). In contrast, the association was largely flat in those with eGFR <60 mL/min/1.73 m2 (n = 233) with P-for-interaction 0.03. Among bone-mineral metabolism markers, only higher iPTH showed an interaction with kidney function (P-for-interaction 0.01) and iPTH >65 pg/mL was significantly related to PAD only in those with eGFR <60 mL/min/1.73 m2.

CONCLUSIONS

Lower magnesium was independently associated with incident PAD, but this association was significantly weaker in those with reduced kidney function. In contrast, higher iPTH levels were particularly related to PAD risk in this clinical population.

High serum magnesium levels are associated with favorable prognoses in diabetic hemodialysis patients, retrospective observational study

Background

Recent studies have found hypomagnesemia is linked to a heightened risk of cardiovascular events and mortality in hemodialysis (HD) patients; however, the level of serum magnesium (s-Mg) necessary for promoting overall health in these patients and the effects of s-Mg in diabetes HD patients remains to be clarified.

Methods

HD outpatients (n = 148 under, age ≤ 70 y) were followed over a 6-y period. They were divided into four groups according to their average s-Mg during the first year (L; low level, H; high level) and if they had DM or not (non-DM). The endpoint was mortality and hospitalization for decline of Activities of Daily Living (death/hospitalization). A receiver operating characteristics curve was used in diagnostic tests to identify s-Mg associated with this endpoint. Kaplan–Meier, log-rank test, and a Cox proportional hazards model were used to evaluate prognoses. Fisher's exact test and multiple regressions examined the causes of the endpoints between the four groups and the factors predictive of s-Mg.

Results

s-Mg at 2.7 mg/dL was associated with death/hospitalization. The 5-y survival rate was 38.1%, 86.7%, 73.2% and 87.5%, in the DM/Mg(L), DM/Mg(H), non-DM/Mg(L) and non-DM/Mg(H) groups, respectively (P < 0.001). The Cox proportional hazards model showed significantly lower risk in other groups compared with that in the DM/Mg(L) group [DM/Mg(H); hazard ratio (HR): 0.22, 95% confidence interval (CI): 0.05–0.97, P = 0.046, non-DM/Mg(L); HR: 0.32, 95% CI: 0.15–0.68, P = 0.003, non-DM/Mg(H); HR: 0.17, 95% CI: 0.06–0.44, P < 0.001]. The frequency of the different causes of the endpoints for each group was not significant; s-Mg only associated with age in the DM group.

Conclusions

s-Mg greater than 2.7 mg/dL associated with a favorable prognosis in HD patients with DM, suggesting that s-Mg is a factor independent of diabetes.

Magnesium Replacement to Protect Cardiovascular and Kidney Damage? Lack of Prospective Clinical Trials

Patients with advanced chronic kidney disease exhibit an increase in cardiovascular mortality. Recent works have shown that low levels of magnesium are associated with increased cardiovascular and all-cause mortality in hemodialysis patients. Epidemiological studies suggest an influence of low levels of magnesium on the occurrence of cardiovascular disease, which is also observed in the normal population. Magnesium is involved in critical cellular events such as apoptosis and oxidative stress. It also participates in a number of enzymatic reactions. In animal models of uremia, dietary supplementation of magnesium reduces vascular calcifications and mortality; in vitro, an increase of magnesium concentration decreases osteogenic transdifferentiation of vascular smooth muscle cells. Therefore, it may be appropriate to evaluate whether magnesium replacement should be administered in an attempt to reduce vascular damage and mortality in the uremic population In the present manuscript, we will review the magnesium homeostasis, the involvement of magnesium in enzymatic reactions, apoptosis and oxidative stress and the clinical association between magnesium and cardiovascular disease in the general population and in the context of chronic kidney disease. We will also analyze the role of magnesium on kidney function. Finally, the experimental evidence of the beneficial effects of magnesium replacement in chronic kidney disease will be thoroughly described.