An increased mortality risk is associated with abnormal iron status in diabetic and non-diabetic Veterans with predialysis chronic kidney disease

Iron parameters have not been well characterized in predialysis patients with chronic kidney disease (CKD), and it remains unclear if abnormal iron balance is associated with increased mortality. Therefore, we performed a historical cohort study using data from the Veterans Affairs Corporate Data Warehouse to evaluate the relationship between iron status and mortality. We identified a predialysis CKD cohort with at least one set of iron indices between 2006-2015. The cohort was divided into four iron groups based on the joint quartiles of serum transferrin saturation (percent) and ferritin concentration (ng/ml): reference (16-28%, 55-205 ng/ml), low iron (0.4-16%, 0.4-55 ng/ml), high iron (28-99.6%, 205-4941 ng/ml), and function iron deficiency (0.8-16%, 109-2783 ng/ml). We compared mortality risk between the iron groups using matching weights based on multinomial propensity score models and Poisson rate-based regression. We also evaluated if the association between iron groups and mortality differs between the diabetic and non-diabetic subgroups. Of the 80,067 eligible veterans, 32,489 were successfully matched. During the mean follow-up period of 4.0 years, adjusted relative rate (95% confidence interval) for all-cause mortality in three abnormal iron groups were increased compared to the reference: functional iron deficiency [1.21 (1.17, 1.25)], low iron [1.10 (1.07, 1.14)], and high iron [1.09 (1.06, 1.13)]. The mortality risk was similar between diabetic and non-diabetic subgroups for each iron group. Thus, an abnormal iron balance, particularly functional iron deficiency, is associated with increased mortality in CKD.