Red Cell Distribution Width and Mortality in Hemodialysis Patients

BACKGROUND: Red cell distribution width (RDW) is an index of red blood cell volume variability that has historically been used as a marker of iron-deficiency anemia. More recently, studies have shown that elevated RDW is associated with higher mortality risk in the general population. However, there is lack of data demonstrating the association between RDW and mortality risk in hemodialysis (HD) patients. We hypothesized that higher RDW levels are associated with higher mortality in HD patients. STUDY DESIGN: Retrospective observational study using a large HD patient cohort. SETTING & PARTICIPANTS: 109,675 adult maintenance HD patients treated in a large dialysis organization January 1, 2007–December 31, 2011. PREDICTOR: Baseline and time-varying RDW, grouped into 5 categories: <14.5%, 14.5%–<15.5%, 15.5%–<16.5%, 16.5%–<17.5% and ≥ 17.5%. RDW 15.5%–<16.5% was used as the reference category. OUTCOME: All-cause mortality. RESULTS: The mean age of study participants was 63±15 (SD) years and the study cohort was 44% female. In baseline and time-varying analyses, there was a graded association between higher RDW levels and incrementally higher mortality risk. Receiver operating characteristic, net reclassification analysis and integrated discrimination improvement analyses demonstrated that RDW is a stronger predictor of mortality as compared with traditional markers of anemia such as hemoglobin, ferritin, and iron saturation. LIMITATIONS: Lack of comprehensive data that may be associated with both RDW and HD patient outcomes, such as blood transfusion data, socioeconomic status, and other unknown confounders; therefore the possibility of residual confounding could not be excluded. Also, lack of information on cause of death; thus, cardiovascular mortality outcomes could not be examined. CONCLUSIONS: In HD patients, higher RDW levels are associated with incrementally higher mortality risk. RDW is also a stronger predictor of mortality than traditional laboratory markers of anemia. Further studies are needed to determine the mechanisms underlying the association between RDW and mortality