Why minorities live longer on dialysis: an in-depth examination of the Danish nephrology registry

NDT Advance Access published January 6, 2016 Nephrol Dial Transplant (2016) 0: 1–4 doi: 10.1093/ndt/gfv419 In Focus Why minorities live longer on dialysis: an in-depth examination of the Danish nephrology registry Harold Simmons Center for Kidney Disease Research and Epidemiology, Division of Nephrology and Hypertension, University of California Irvine, Orange, CA, USA and 2 David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA, USA Correspondence and offprints requests to: Connie M. Rhee; E-mail: crhee1@uci.edu Epidemiological data have consistently shown that various ra- cial and ethnic minorities, including black, Hispanic, Indo- Asian and Arab-Israeli populations, have a disproportionately higher prevalence of end-stage renal disease (ESRD) compared with those of white European ancestry [1–3]. Among minorities with ESRD, numerous disparities have been observed, including less access to pre-ESRD nephrology care, poorer achievement of dialysis performance measures (e.g. hemoglobin and parathyroid hormone levels) and lower kidney transplantation rates [4–6]. Despite these inequities, population-based studies show that racial/ethnic minorities receiving dialysis have a paradoxical survival advantage compared with their white counterparts [1, 2, 5, 7–9]. While these racial/ethnic differences in ESRD survival have been well documented in US and Canadian-based popula- tions, there have been few studies of European dialysis patients, and these have largely been restricted to populations in the UK and The Netherlands (Table 1) [3, 10–14]. Further examination of dialysis populations from other countries of the European Union are warranted, given their (i) disparate racial/ethnic com- positions, (ii) lower comorbidity burden and mortality rates, (iii) differential age distributions and (iv) distinct health care delivery systems across different European Union nations. In this issue of Nephrology Dialysis Transplantation, van den Beukel et al. [14] conducted one of the largest European-based studies of race, ethnicity and survival among incident dialysis patients to date using the Danish National Registry, which has comprehensive capture of all Danish ESRD patients from 1990 onward. The investigators granularly examined the sur- vival of various immigrant racial/ethnic populations and found that all immigrant subgroups had lower mortality risk compared with native Danes in crude and adjusted analyses. Linkage of patient-level data to Statistics Denmark, a Danish governmental organization under the Ministry for Economic © The Author 2016. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved. and Interior Affairs, also permitted examination of the associ- ation between the duration of residence and death risk among immigrants, which demonstrated that in Western immigrants, the survival beneﬁt attenuated over time but remained robust among those of non-Western origin [14, 15]. Access to the Danish Nephrology Registry allows for in- depth examination of the entire Danish incident dialysis population, from whom inferences can be drawn without sub- stantial selection or survivor bias. For example, the study’s low proportion of immigrant dialysis patients (∼9%) was similar to that of the broader Danish population (∼7%), and was largely comprised of patients of Western, Arab, South and Southeast Asian and sub-Saharan African origin [14, 15]. The predominantly white population, in conjunction with the relatively low burden of diabetes as the primary cause of ESRD (23%), may account for Denmark’s decline in ESRD over the past decade [incidence rates of treated ESRD patients as of 2000 and 2013 were 132 and 117 per million, respectively, according to longitudinal international data from the United States Renal Data System (USRDS)] [1]. Another notable ob- servation was the similar age-adjusted rates of kidney trans- plantation among immigrant subgroups and native Danes, which stands in contrast to other Western nations, where black and Hispanic dialysis patients are less likely to undergo transplantation [1, 5]. Given their equivalent transplant rates, it is unlikely that the diminution of healthier native Danish dialysis patients due to kidney transplantation is an explana- tory factor for lower mortality risk among immigrants; in addition, competing risk methods used to address differential transplantation rates across race/ethnicity demonstrated a robust immigrant survival advantage. Direct study of the Danish dialysis population also pro- vides a unique opportunity to dissect potential mechanisms Downloaded from http://ndt.oxfordjournals.org/ at University of California, Los Angeles on January 7, 2016 Connie M. Rhee 1 , Kamyar Kalantar-Zadeh 1 and Keith C. Norris 2