Chronic kidney disease (CKD) is a major contributor to premature morbidity and mortality. There are variations in the estimated prevalence of CKD by racial and/or ethnic (racial/ethnic) group and by geographic location. Previous studies have identified ethnic subgroup differences for Hispanics, with a nearly two-fold difference across individuals of Cuban (12%), Mexican (13%), Puerto Rican (17%), and South American (8%) backgrounds. In the United States, racial/ethnic minorities are more likely to develop end-stage renal disease (ESRD) than nonminority groups, and are often treated with maintenance dialysis.
There are numerous data on the incidence of CKD and ESRD in the United States; however, data regarding kidney disease in United States territories are limited. The US Renal Data System (USRDS) focuses primarily on individuals in the 50 states. There are five US territories: Puerto Rico, the US Virgin Islands, Guam, the Northern Mariana Islands, and American Samoa.
The proportions of diabetes-related ESRD are high in those territories. There are few available data on mortality outcomes of patients undergoing dialysis in the territories. To test the hypothesis that mortality outcomes for patients in the territories may differ from those in the 50 states, Guofen Yan, PhD, and colleagues conducted a national population study to examine all-cause mortality by racial/ethnic group among patients with ESRD treated with dialysis in the US territories compared with patients treated in the 50 states. Results were reported in the Clinical Journal of the American Society of Nephrology [2020;15:101-108].
The outcomes of interest were mortality differences between patients undergoing dialysis in the US territories and those in the 50 states in the same racial/ethnic group. Hazard ratios (HRs) of death for the territories versus 50 states for each racial/ethnic group using the whole cohort and covariate-matched samples were calculated using Cox proportional hazards regression.
The researchers used the USRDS Core Standard Analysis Files to identify all patients ≥18 years of age with no prior kidney transplantation who initiated maintenance dialysis between April 1, 1995, and September 28, 2012. Exclusion criteria were missing body mass index data and missing data on estimated glomerular filtration rate.
The final analysis cohort consisted of 1,547,438 patients, including 22,828 patients in the four territories (295 in American Samoa, 1507 in Guam [including the Northern Mariana Islands], 20,289 in Puerto Rico, 737 in the Virgin Islands) and 1,524,610 nonterritory patients (50 states).
Of those in the 50 states, 55% (n=838,736) were white, 29% (n=444,066) were black, 12% (n=182,994) were Hispanic, and 4% (n=58,814) were Asian. Of the 22,828 patients in the territories, 1% (n=321) were white, 3% (n=666) were black, 89% (n=20,299) were Hispanic, and 7% (n=1542) were Asian.
On average, white and Asian patients in the territories were 7 years and 4 years younger, respectively, compared with their counterparts in the 50 states; black and Hispanic patients in the territories were an average of 2 years older than their counterparts in the 50 states. The patients in the territory cohort had a higher prevalence of diabetes-related ESRD (64% vs 45%) and were less likely to have pre-ESRD erythropoietin use (20% vs 27%), a nephrology visit prior to dialysis initiation (50% vs 58%), or use of an arteriovenous fistula (10% vs 14%).
Average BMIs were similar among white, black, and Hispanic groups in both cohorts; Asians in the territories had higher BMIs compared with Asians in the 50 states (28 vs 25 kg/m2). There were also some patient characteristics that varied across the four territories; Samoans tended to have higher BMIs and Puerto Ricans were more likely to have received predialysis erythropoietin compared with those in the other territories, for example.
Median follow-up time for the territory group was 23 months; for the 50 states median follow-up was 25 months. In the territories, white patients undergoing dialysis had a much lower crude mortality rate compared with their counterparts in the 50 states: 14 vs 29 deaths per 100 patient-years). Mortality rates among black patients were similar: 18 per 100 patient-years in the territories versus 17 per 100 patient-years in the 50 states. In contrast, mortality rates among Hispanics in the territories were much higher than among their counterparts in the 50 states: 27 versus 16 per 100 patient-years (27 deaths per 100 patient-years for Puerto Rican Hispanics alone and 24 deaths per 100 patient-years for Virgin Island Hispanics alone). The mortality rate in the territories among Asians was also higher than among their counterparts in the 50 states.
In both the territories and the 50 states groups, the major cause of death was cardiovascular disease. Regardless of race and ethnicity, the percentages of death from infection were consistently greater in the territories than in the 50 states.
Following adjustment for demographic and clinical characteristics, the mortality risk for white patients in the territories remained lower than that among white patients in the 50 states (hazard ratio [HR], 0.75; 95% confidence interval [CI], 0.65-0.86; P<.001); there was no difference in the mortality risk between the two groups for black patients (HR, 1.04; 95% CI, 0.94-1.15; P=.45). In contrast, the risks for death among Hispanic and Asian patients in the territories remained higher (HR, 1.61; 95% CI, 1.58-1.63; P<.001 and HR, 1.95; 95% CI, 1.82-2.08; P<.001, respectively).
Limitations to the findings cited by the authors included differences in payer mix and structure in the territories and the 50 states, the lack of data to identify specific Hispanic and Asian subgroups in the USRDS, the relatively low number of dialysis patients in most of the territories other than Puerto Rico, and not including data from 2013-2016.
In summary, the researchers said, “To our knowledge, this study is the first to document important differences in dialysis mortality for various racial/ethnic groups in the territories versus the 50 states. We found notable higher mortality rates for Hispanic and Asian patients undergoing dialysis in the territories than their counterparts in the 50 states. Mortality risk did not appear to differ between the territories and the 50 states for whites or blacks. Further studies are needed to better understand the influence of issues such as genetic factors, insurance coverage, health infrastructure, health beliefs and behaviors, social networks, and other subtleties in the United States territories that may add critical insights to our observations.”
Takeaway Points
- Researchers conducted a retrospective cohort study to examine all-cause mortality by racial/ethnic group among dialysis patients in the United States territories versus dialysis patients in the 50 states.
- The crude mortality rate (deaths per 100 patient-years) was lower for white patients in the territories versus the 50 states (14 and 29, respectively) and similar for black patients (18 and 17, respectively).
- The crude mortality rate was higher for Hispanic and Asian patients in the territories than in the 50 states (27 and 16 per 100 patient-years, respectively, and 22 and 15 per 100 patient-years, respectively).
