Impact of admission serum magnesium levels on long-term mortality in hospitalized patients

BACKGROUND The impact of admission serum magnesium on long-term mortality in hospitalized patients was unclear. This study aimed to assess the long-term mortality risk based on admission of serum magnesium in hospitalized patients. METHODS This was a retrospective cohort study conducted at a tertiary referral hospital. We included all adult patients admitted to Mayo Clinic Hospital, Minnesota, between 1 January 2009 and 31 December 2013, who had available admission serum magnesium. We categorized serum magnesium into ≤1.4, 1.5-1.6, 1.7-1.8, 1.9-2.0, 2.1-2.2, ≥2.3 mg/dL. We estimated the 1-year mortality risk based on various admission serum magnesium levels using Kaplan-Meier plot and assessed the association of admission serum magnesium with 1-year mortality using Cox proportional hazard analysis. We selected serum magnesium of 1.7-1.8 mg/dL as the reference group for mortality comparison. RESULTS We included a total of 65,974 patients, with a mean admission serum magnesium of 1.9 ± 0.3 mg/dL in this study. The 1-year mortality was 15.7%, 15.8%, 15.5%, 16.7%, 19.0%, and 25.6% in admission serum magnesium of ≤1.4, 1.5-1.6, 1.7-1.8, 1.9-2.0, 2.1-2.2, ≥2.3 mg/dL, respectively (p < 0.001). After adjustment for confounders, admission serum magnesium of 1.9-2.0, 2.1-2.2, and ≥2.3 mg/dL were significantly associated with increased 1-year mortality compared with magnesium of 1.7-1.8 mg/dL with adjusted HR of 1.09 (95% CI 1.02-1.15), 1.22 (95% CI 1.14-1.30), and 1.55 (95% CI 1.45-1.55), respectively. There was no significant difference in 1-year mortality risk between low serum magnesium ≤1.6 mg/dL and magnesium of 1.7-1.8 mg/dL. CONCLUSION Hypermagnesemia, but not hypomagnesemia, at the time of hospital admission was associated with increased 1-year mortality among hospitalized patients.