Variability of ferritin measurements in chronic kidney disease; implications for iron management

Serum ferritin levels are a proxy measure of iron stores; existing guidelines for managing anemia in hemodialysis patients suggest that serum ferritin concentrations should be maintained at > 200 ng/ml. The KDOQI recommendations further state there is insufficient evidence advocating routine intravenous iron when ferritin levels exceed 500 ng/ml. Here we determined the interassay differences and short-term intraindividual variability of serum ferritin measurements in patients on chronic hemodialysis to illustrate how these variances may affect treatment decisions. Intermethod variations of up to 150 ng/ml were found comparing six commonly used ferritin assays that evaluated thirteen pools of serum from hemodialysis and nonhemodialysis patients. The intraindividual variability for ferritin in 60 stable hemodialysis patients ranged between 2-62% measured over an initial two-week period and from 3-52% when factored over a six-week period. Our results suggests that single serum ferritin values should not be used to guide clinical decisions regarding treatment of chronic hemodialysis patients with intravenous iron due to significant analytical and intraindividual variability.