To the Editor: The retrospective cohort study by Dr Winkelmayer and colleagues1 suggested an inverse relationship between increasing altitude and all-cause mortality among US dialysis patients after adjusting for age, sex, and race in the dialysis population. Race and ethnicity have been shown to be associated with differences in all-cause and disease-specific mortality.2 - 3 In addition to differences in risk factors and genetic influences, mortality rates reflect in part racial and ethnic differences associated with health care access and quality.4
Because of the lower prevalence of most comorbid conditions as altitude increases, lower proportion of African American and Asian patients at higher altitudes, and higher proportion of Native Americans residing at higher altitudes, the authors appropriately adjusted for race in their estimates of all-cause mortality in the dialysis patients. However, although the mortality rates by altitude for the dialysis patients were adjusted for age, sex, and race, the comparative general population mortality rates were standardized only for age and sex.
The failure to adjust for race in the general population mortality rates may result in underestimation of the mortality rate in the general population residing at lower altitudes. An increase in the race-adjusted general population rates may result in statistically nonsignificant differences (overlap of confidence intervals) when comparing the general population and the end-stage renal disease (ESRD) population, therefore decreasing the likelihood that these 2 groups are truly different. The authors had emphasized the lack of overlap of the confidence intervals when interpreting the significance of their findings.
Another concern is that if for a specific disease a patient's prognosis or quality of life is adversely affected by altitude, that may affect the choice of where to live. If these diseases are associated with race and with increased mortality (eg, sickle cell disease), the apparent protective effect on all-cause general mortality rates by increasing altitude may be confounded by these associations. Information on mortality rates for specific conditions and the number of deaths from these comorbid conditions by race would strengthen and help interpret the study results.
Financial Disclosures: None reported.
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
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