Serum Magnesium Levels and Hospitalization and Mortality in Incident Peritoneal Dialysis Patients: A Cohort Study

Abstract

Background: Prior studies have shown the association of low serum magnesium levels with adverse health outcomes in patients undergoing hemodialysis. There is a paucity of such studies in patients undergoing peritoneal dialysis (PD).

Study design: Cohort study.

Setting & participants: 10,692 patients treated with PD from January 1, 2007, through December 31, 2011, in facilities operated by a single large dialysis organization in the United States.

Predictor: Baseline serum magnesium levels, examined as 5 categories (<1.8, 1.8-<2.0, 2.0-<2.2 [reference], 2.2-<2.4, and ≥2.4mg/dL).

Outcomes: Time to first hospitalization and time to death using competing-risks regression models.

Results: The distribution of baseline serum magnesium levels in the cohort was <1.8mg/dL, 1,928 (18%); 1.8 to <2.0mg/dL, 2,204 (21%); 2.0 to <2.2mg/dL, 2,765 (26%); 2.2 to <2.4mg/dL, 1,765 (16%); and ≥2.4mg/dL, 2,030 (19%). Of 10,692 patients, 6,465 (60%) were hospitalized at least once and 1,392 (13%) died during follow-up (median, 13; IQR, 7-23 months). Baseline serum magnesium level < 1.8mg/dL was associated with higher risk for hospitalization and all-cause mortality after adjustment for demographic and clinical characteristics (adjusted HRs of 1.23 [95% CI, 1.14-1.33] and 1.21 [95% CI, 1.03-1.42], respectively). The higher risk for hospitalization persisted upon adjustment for laboratory variables, whereas that for all-cause mortality was attenuated to a nonsignificant level. The greatest risk for hospitalization was in patients with low serum albumin levels (<3.5g/dL; P for interaction < 0.001).

Limitations: Possibility of residual confounding by unmeasured variables cannot be excluded.

Conclusions: Lower serum magnesium levels may be associated with higher risk for hospitalization in incident PD patients, particularly those with hypoalbuminemia. Additional studies are needed to confirm these findings and investigate whether correction of hypomagnesemia reduces these risks.

Keywords: Magnesium; all-cause mortality; end-stage renal disease (ESRD); hospitalization; hypomagnesemia; incident PD patients; peritoneal dialysis (PD).

Figure 1. Flow chart summarizing how the cohort was assembled

Abbreviations: PD, peritoneal dialysis; Mg, magnesium.

Figure 2. The distribution of average serum Mg over the first 3 months of peritoneal dialysis (n=10,692)

The data reflect the averaged measurements made during the first 3 months of PD treatment.

Figure 3. Hazard ratios for hospitalization by categories of baseline serum magnesium (reference: serum magnesium, 2.0 – < 2.2 mg/dl)

Competing risks regression models with 3 levels of adjustments:(1) unadjusted; (2) case-mix adjusted for age, gender, diabetes, race/ethnicity, primary insurance, geographic location, year of incidence, cause of end-stage renal disease, prior kidney transplant, comorbid conditions (hypertension, congestive heart failure, atherosclerotic heart disease, other cardiovascular diseases), and interval from initiation of dialysis to initiation of peritoneal dialysis; and (3) case-mix and laboratory data (hemoglobin, albumin, uncorrected calcium, phosphorus, intact parathyroid hormone, ferritin, iron saturation, bicarbonate, potassium, total weekly Kt/V urea, residual kidney function, D/P creatinine, use of automated PD).

Figure 4. Association of serum magnesium with time to first hospitalization stratified by serum albumin and residual kidney function among patients treated with peritoneal dialysis

The lines represent hazards ratio for hospitalization for patients with serum magnesium level < 1.8 mg/dl (reference: ≥ 1.8 mg/dl) in the study population stratified by serum albumin (< and ≥ 3.5 g/dl) and residual kidney function (< and ≥ 55 L/week/1.73 m²). Competing risks regression models with 3 levels of adjustments:(1) unadjusted; (2) case-mix adjusted for adjusted for age, gender, diabetes, race/ethnicity, primary insurance, geographic location, year of incidence, cause of end-stage renal disease, prior kidney transplant, comorbid conditions (hypertension, congestive heart failure, atherosclerotic heart disease, other cardiovascular diseases), and interval from initiation of dialysis to initiation of peritoneal dialysis; and (3) case-mix and laboratory data adjusted for all covariates above plus hemoglobin, uncorrected calcium, phosphorus, intact parathyroid hormone, ferritin, iron saturation, bicarbonate, potassium, total weekly Kt/V urea, D/P creatinine, and use of automated PD. The covariate used to stratify the population was not used for additional adjustment – residual kidney function was an additional covariate in analyses stratified by serum albumin and serum albumin in analyses stratified by residual kidney function.

Figure 5. Hazard ratios for all-cause mortality by categories of baseline serum magnesium (reference: serum magnesium, 2.0 – < 2.2 mg/dl)

Competing risks regression models with 3 levels of adjustments:(1) unadjusted; (2) case-mix adjusted for adjusted for age, gender, diabetes, race/ethnicity, primary insurance, geographic location, year of incidence, cause of end-stage renal disease, prior kidney transplant, comorbid conditions (hypertension, congestive heart failure, atherosclerotic heart disease, other cardiovascular diseases), and interval from initiation of dialysis to initiation of peritoneal dialysis; and (3) case-mix and laboratory data adjusted for all covariates above plus hemoglobin, albumin, uncorrected calcium, phosphorus, intact parathyroid hormone, ferritin, iron saturation, bicarbonate, potassium, total weekly Kt/V urea, residual kidney function, D/P creatinine, use of automated PD.