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Abstract

Dr Kamei indicated that the coefficient of variation among ferritin measurements available in Japan is relatively large.1.Kamei D. Coefficient of variation among ferritin measurement in hemodialysis and standard serum ferritin level.Kidney Int. 2015; 88: 197Abstract Full Text Full Text PDF PubMed Scopus (3) Google Scholar As Ford et al.2.Ford B.A. Coyne D.W. Eby C.S. et al.Variability of ferritin measurements in chronic kidney disease; implications for iron management.Kidney Int. 2009; 75: 104-110Abstract Full Text Full Text PDF PubMed Scopus (50) Google Scholar reported, owing to analytical or intra-individual variability, general trends in ferritin determinants over time might be better determinants of the adequacy of iron therapy than the specific ferritin cutoff values. Intra-individual variability: we have also reported that ferritin levels of hemodialysis patients are highly variable.3.Yahiro M. Kuragano T. Kida A. et al.The impact of ferritin fluctuations on stable hemoglobin levels in hemodialysis patients.Clin Exp Nephrol. 2012; 16: 448-455Crossref PubMed Scopus (9) Google Scholar The serum ferritin fluctuation pattern, which is evaluated in this study, is carefully considered in the intra-individual variability of ferritin levels. Analytical variability: for the evaluation of serum ferritin levels, it is best to use an identical method. However, in a large-scale multicenter study, that is sometimes difficult. Although analytical variability might strongly affect the values at a higher range of ferritin, its influence could be small in the lower range. In this study, the serum ferritin level was very low in most of the participants (58% of the patients had levels under 100 ng/ml and 38% had levels under 50 ng/ml). In addition, we evaluated the association between ferritin fluctuation patterns and adverse events but not between specific ferritin cutoff values and adverse events. The serum ferritin level of an individual patient was measured by the same method during the study period. Thus, we presumed that the influence of analytical variability on the results of our study might be negligible. Target hemoglobin (Hb) levels: at first, we set a target Hb level of over 11 g/dl. However, the number of patients who maintained Hb levels over 11 g/dl during the study period was small. In this subanalysis of the Treatment for Renal Anemia on Prognosis in hemodialysis patients study, we set the target Hb level at 10–11 g/dl, which was recommended by the 2008 Japanese Society for Dialysis Therapy: Guidelines for Renal Anemia in Chronic Kidney Disease,4.Tsubakihara Y. Nishi S. Akiba T. et al.2008 Japanese Society for Dialysis Therapy: guidelines for renal anemia in chronic kidney disease.Ther Apher Dial. 2010; 14: 240-275Crossref PubMed Scopus (199) Google Scholar and analyzed the relationship between Hb fluctuation patterns and adverse events or death.