Effect of center- versus patient-specific factors on variations in dialysis adequacy

Efforts to improve the delivery of hemodialysis have focused mostly on identifying patient-related factors that lead to inadequate dialysis. Less consideration has been given to the impact of the dialysis center on adequacy. This study evaluated whether the dialysis facility or individual-level factors were the primary influence on variations in dialysis adequacy. This was a retrospective analysis of 4971 hemodialysis patients in 189 centers with urea reduction ratio (URR) values obtained in the final quarter of 1997. The between-center variation and the within-center correlation in URR values were quantified to determine the contribution of a center effect on variations in adequacy; furthermore, the proportion of variance attributable to the centers' effect and individual-level dialysis covariates were compared. There was a wider between-center variation in mean URR values (SD, 4.8%) than expected if there were no center effect (SD, 2.5%). There was a strong within-center correlation in URR values, measured by the parameter rho, which was only minimally diminished after adjusting for individual-level covariates (adjusted rho, 0.14; P < 0.0001). The variation in URR attributable to the center effect, quantified by R(2), was greater than that related to individual-level dialysis factors (facility- and individual-level dialysis covariates R(2), 23.6 and 11.3%, respectively). Initiatives to improve the delivery of dialysis in patients with end-stage renal disease should be directed at facility policies governing dialysis care, along with patient-specific problems, because center effects have a major influence on dialysis adequacy.