1 Kidney International 2007 Vol: 71(1):11-12. DOI: 10.1038/sj.ki.5001685

Regional mortality differences in end-stage renal disease: How far can observational studies take us?

The survival of patients with ESRD living in various geographic regions is strikingly different. Efforts to determine the reasons behind this observation have been hampered by difficulties in adjusting for many characteristics that are inherently different in patient populations living on different continents. The mortality rate for the general population in a given region could be used to adjust for risk factors that would be otherwise difficult to quantify.

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References
  1. Held PJ, Brunner F, Odaka M et al. Five-year survival for end-stage renal disease patients in the United States, Europe, and Japan, 1982 to 1987. Am J Kidney Dis 1990; 15: 451-457 , .
  2. Young EW, Goodkin DA, Mapes DL et al. The Dialysis Outcomes and Practice Patterns Study (DOPPS): an international hemodialysis study. Kidney Int 2000; 57: S74-S81 , .
    • . . . The Dialysis Outcomes and Practice Patterns Study (DOPPS) offered the ideal remedy for this problem, as it uniformly recorded patient outcomes from dialysis units in Europe, Japan, and the United States, and it was also able to describe the characteristics of the different patient populations in extensive detail.2 Not unexpectedly, it became clear that all ESRD patients are not equal: racial composition in various geographical areas is obviously different, and patients in the United States are older and have a higher burden of comorbidities.3 Detailed adjustment for this heterogeneity alleviated somewhat the transcontinental mortality gap, but the difference remained significant nevertheless, again suggesting that variability in individual patient characteristics alone is not sufficient to explain the observed geographical diversity.3 . . .
  3. Goodkin DA, Bragg-Gresham JL, Koenig KG et al. Association of comorbid conditions and mortality in hemodialysis patients in Europe, Japan, and the United States: the Dialysis Outcomes and Practice Patterns Study (DOPPS). J Am Soc Nephrol 2003; 14: 3270-3277 , .
  4. van Dijk PCW, Zwinderman AH, Dekker FW et al. Effect of general population mortality on the north-south mortality gradient in patients on replacement therapy in Europe. Kidney Int 2007; 71: 53-59 , .
    • . . . Van Dijk et al.4 (this issue) offer a simple and elegant solution to this problem: they used general population mortality rates as surrogate adjustment for a host of difficult-to-measure factors, assuming that all or most of these factors have a similar impact on people living in the same area, including patients with ESRD . . .
    • . . . Detailed patient characteristics were not available in the study by van Dijk et al.;4 hence it is unclear what caused the remaining difference . . .
    • . . . It is unclear how valid such an approach would be in comparing large entities (such as mortality in Europe versus Japan versus the United States), given the clearly significant regional variations in both ESRD and general population mortality rates within these entities.3, 4, 5 It is also unclear how the logic of using general population mortality to alleviate the differences in ESRD mortality across continents would apply in the case of the United States, where ESRD mortality is highest (when compared with those of Japan and Europe) and yet general population mortality is lower than that reported in Europe.1 . . .
    • . . . The study by van Dijk et al.4 has brought renewed attention to a tool that could enhance similar studies . . .
  5. Wong JS, Port FK, Hulbert-Shearon TE et al. Survival advantage in Asian American end-stage renal disease patients. Kidney Int 1999; 55: 2515-2523 , .
    • . . . Interestingly, though, the general population mortality in the United States was found to be lower than that in Europe, thus magnifying rather than alleviating the differences noted between ESRD mortality rates in these two regions.1 A more detailed analysis of this kind was used by Wong et al.,5 who compared ESRD mortality in Asian Americans versus other races in the United States and showed that race-specific general population death rates explained more than half of the variation in mortality imparted by race . . .
    • . . . It is unclear how valid such an approach would be in comparing large entities (such as mortality in Europe versus Japan versus the United States), given the clearly significant regional variations in both ESRD and general population mortality rates within these entities.3, 4, 5 It is also unclear how the logic of using general population mortality to alleviate the differences in ESRD mortality across continents would apply in the case of the United States, where ESRD mortality is highest (when compared with those of Japan and Europe) and yet general population mortality is lower than that reported in Europe.1 . . .