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

Abstract

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 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 January 1st, 2009 and December 31st, 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.