New parameters in iron metabolism and functional iron deficiency in patients on maintenance hemodialysis.

INTRODUCTION: Iron metabolism has been studied for many years. New substances involved in iron metabolism continue to be described. Functional iron deficiency (FID) is characterized by the presence of adequate iron stores (as defined by standard criteria) but insufficient iron mobilization required for erythropoiesis during administration of erythropoiesis-stimulating agents.
OBJECTIVES: The aim of the study was to evaluate new parameters of iron metabolism and the prevalence of FID as well as to assess potential correlations in patients on hemodialysis (HD). PATIENTS AND METHODS: The study included 98 patients on maintenance HD. Standard laboratory methods were used to measure the iron status, complete blood count, creatinine, calcium, phosphorus, albumin, intact parathyroid hormone, and lipids. Commercially available kits were used to measure high-sensitivity C-reactive protein (hsCRP), interleukin 6 (IL-6), tumor necrosis factor-α, N-terminal pro-B-type natriuretic peptide (NT-proBNP), growth differentiation factor (GDF15), bone morphogeneticprotein (BMP6), hemojuvelin, and hepcidin.
RESULTS: FID was present in 23% of the patients on HD and was associated with significantly higher serum ferritin, IL-6, hsCRP, hepcidin, and NT-proBNP levels. There were no significant differences in BMP6 and GDF15 levels between patients with and without FID. Patients on HD had increased prevalence of hypertension, diabetes, and left ventricular hypertrophy and required slightly, but insignificantly, higher erythropoietin doses. Predictors of FID included serum iron levels and residual renal function.
CONCLUSIONS: FID is present in a substantial proportion of patients on HD, who thus should be screened for reversible causes of inflammation. New parameters in iron metabolism do not seem to be related to FID in patients on HD.