Magnesium is a co-factor in natural killer and T cell reactivity and may modify the course of infections. We examined the association between baseline serum magnesium concentration and infections requiring admission the first year after kidney transplantation.

Inclusion of adults transplant recipients between January 2003 and 31 December 2013. Cox piecewise linear regression model estimating the hazard ratio for first admission for infection. Outcomes until one year post-transplantation or up to May 1, 2014.

Overall, 371 of 873 persons were admitted at least once the first year after transplantation (65 events per 100 person-years). The infection-specific cumulative incidence increased with lower serum magnesium concentration (P = 0.008). After adjustment for confounders, a low serum magnesium was associated with an increased hazard of infection (P < 0.0001 in type 3 test). With 2 mg/dL as the reference value, every 0.1 mg/dL reduction in serum magnesium at baseline below 2 mg/dL (N = 165) increased the hazard ratio by 15% (HR 1.15, 95%CI 1.05–1.27; P = 0.002) while every increase of 0.1 mg/dL in those with a serum magnesium between 2 and 3 mg/dL (N = 661) decreased the hazard ratio by 4% (HR 0.96, 95%CI 0.93–1.00; P = 0.08).

A lower baseline serum magnesium concentration is associated with an increased risk of infection after kidney transplantation.