Abstract
Background and objectives Data on racial disparities in home dialysis utilization and outcomes are lacking in Canada, where health care is universally available.
Design, setting, participants, & measurements We studied patients starting maintenance dialysis between 1996 and 2012 in the Canadian Organ Replacement Register, stratified by race: white, Asian, black, Aboriginal, Indian subcontinent, and other. The association between race and treatment with home dialysis was examined using generalized linear models. Secondary outcomes assessed racial differences in all-cause mortality and technique failure using a Fine and Gray competing risk model.
Results 66,600 patients initiated chronic dialysis between 1996 and 2012. Compared with whites (n=46,092), treatment with home dialysis was lower among Aboriginals (n=3866; adjusted relative risk, RR, 0.71; 95% confidence interval, CI, 0.66 to 0.76) and higher in Asians (n=4157; adjusted RR, 1.28; 95% CI, 1.22 to 1.35) and others (n=2170; adjusted RR, 1.12; 95% CI, 1.04 to 1.20) but similar in blacks (n=2143) and subcontinent Indians (n=2809). Black (adjusted hazard ratio, HR, 1.31; 95% CI, 1.16 to 1.48) and Aboriginal (adjusted HR, 1.19; 95% CI, 1.06 to 1.33) patients treated with peritoneal dialysis had a significantly higher adjusted risk of technique failure compared with whites, whereas Asians had a lower risk (adjusted HR, 0.89; 95% CI, 0.82 to 0.99). In patients on peritoneal dialysis, the risk of death was significantly lower in Asians (adjusted HR, 0.83; 95% CI, 0.75 to 0.92), blacks (adjusted HR, 0.71; 95% CI, 0.59 to 0.85), and others (adjusted HR, 0.79; 95% CI, 0.68 to 0.92) but higher in Aboriginals (adjusted HR, 1.16; 95% CI, 1.02 to 1.32) compared with whites. Among patients on home hemodialysis, no significant racial differences in patient and technique survival were observed, which may be limited by the low number of events among each subgroups.
Conclusions With the exception of Aboriginals, all racial minority groups in Canada were as likely to be treated with home dialysis compared with whites. However, significant racial differences exist in outcomes.
- ethnicity
- ethnic disparities
- home dialysis
- home hemodialysis
- patient survival
- race
- racial disparities
- technique survival
- Hemodialysis, Home
- Minority Groups
- Linear Models
- Canada
- European Continental Ancestry Group
- African Continental Ancestry Group
- peritoneal dialysis
- Asian Continental Ancestry Group
Introduction
Home dialysis modalities, including home hemodialysis (HD) and peritoneal dialysis (PD), are associated with increased patient autonomy, improved patient satisfaction, and lower costs compared with facility-based HD (1–4). Despite these advantages, home dialysis modalities remain underused, with varying degrees of representation across racial groups (5–9). A recent study from Mehrotra et al. (6) highlighted racial disparities in the use of home dialysis in the United States, with nonwhite patients significantly less likely to be treated with home dialysis compared with whites. Furthermore, clinical outcomes also seem to differ across different racial groups, with studies showing a lower mortality risk among some racial minorities but also, a lower likelihood of receiving a kidney transplant compared with whites (6,7,10–12).
Given the potential benefits with home dialysis modalities, racial disparities in home dialysis utilization need to be further elucidated, and modifiable factors need to be identified. Potential causes for these disparities include patient preferences, education level, employment status, socioeconomic status, physician experience, access to predialysis care, and availability of home dialysis modalities in nearby facilities. Environmental factors and health care delivery may equally play a role. Nonetheless, data on racial disparities in home dialysis utilization and outcomes in the setting of a public health care system are lacking. It is tempting to speculate that racial differences in home dialysis utilization and outcomes may be different compared with the findings in the United States for several reasons. Unlike the United States, Canada has universal government-funded health care coverage across all stages of CKD (13). Although nonwhites do represent more than one fifth of the Canadian population, the racial composition of the population differs from that of the United States, with Asians accounting for the largest minority group, a larger Indigenous population, and a lower proportion of blacks (14). Lastly, home dialysis utilization is higher in Canada compared with the United States, achieved in 20%–25% of the ESRD population (15). Given these differences in population and health care delivery, our primary aim was to examine if racial disparities exist in the use of home dialysis modalities in Canada. Our secondary aims were to assess the association between race and patient and technique survival in patients on home dialysis.
Materials and Methods
This registry-based observational cohort study included adult patients (ages ≥18 years old at time of dialysis initiation) who initiated their first form of dialysis in Canada between January 1, 1996 and December 21, 2012. Data were analyzed from the Canadian Organ Replacement Register (CORR), a national registry that captures the incidence, prevalence, and outcomes of >99% of patients on chronic dialysis and solid organ transplant recipients in Canada and has been validated (16,17). The data were collected by completion of a registration form for each patient by the dialysis provider at initiation of dialysis and yearly thereafter. Data from the province of Quebec were excluded due to the need for additional ethics and data permissions. The research study protocol was approved by the CORR.
Patients (n=61,237) were divided into six groups according to race: white, Asian, black, Aboriginal, Indian subcontinent, and other. Although the term indigenous has also been used to describe individuals of First Nations, Inuit, and Métis origin, we chose to use the term Aboriginal, because it is the terminology used in the CORR. Furthermore, the term “Caucasian” was used in the CORR to describe white individuals. Baseline comorbidities were documented by the individual facilities using the CORR registration form at the time of dialysis initiation. Data on race were completed by the health care provider at time of initiation of dialysis, with likely variable and inconsistent input from the patient. Vascular access type was also ascertained at the time of first dialysis. Late referral was defined as never having been seen by a nephrologist before dialysis initiation or first seeing a nephrologist within 3 months before starting dialysis. Distance to nearest dialysis center was calculated as the direct linear distance in kilometers from the patient’s residence using postal code to the nearest dialysis center at the time of first dialysis. Income was calculated using median neighborhood income, classified by quintiles, as a measure of socioeconomic status. These income data were compiled by linking Statistics Canada census data with postal codes for patients’ residences. Facility center size was categorized as follows: small (one to ten patients), medium (11–55 patients), and large (>55 patients). Patients were considered as having ever been treated with PD or home HD if they were assigned to this renal replacement modality during follow-up. Patients were labeled in the in-center HD group if they were treated exclusively with conventional in-center HD during follow-up.
Outcomes
The primary outcome was the association of race with having ever been treated with a home dialysis modality (PD or home HD). Secondary outcomes assessed racial differences in clinical outcomes for each home dialysis modality (PD and home HD), including time to all-cause mortality and technique failure. The composite outcome of all-cause mortality and technique failure was also examined. Technique failure was defined as a transfer to another renal replacement modality for 60 days or longer.
Statistical Analyses
Baseline demographics and clinical characteristics are presented as means±SD, medians and interquartile ranges, or proportions as appropriate. The associations between different racial groups and treatment with a home dialysis modality were examined using generalized linear models, where risk ratios of home modality usage were calculated by selecting Poisson as the underlying probability distribution and logarithm as a link function. The proportional hazards models for the subdistribution of Fine and Gray (18) were used to compare time to all-cause mortality and technique failure among different racial groups, which were analyzed separately in each of the two home dialysis modalities (home HD and PD). A Fine and Gray (18) model allowed us to adjust for the effect of informative censoring caused by potential differences in rates of kidney transplantation among different racial groups. Censoring events for the analysis of mortality and technique failure included loss to follow-up or being alive at the end of the observation period, whereas transplantation was treated as a competing risk that can impede the outcome events of interest. Models were first adjusted for clinical characteristics, including age, sex, body mass index, cause of ESRD, and comorbidities. Subsequently, fully adjusted models included both clinical characteristics and socioeconomic factors (distance from dialysis center, facility size, income quintile, region within Canada, and era). Additionally, for the secondary outcomes of time to mortality and technique failure, timing of initiation of PD/home HD and type of PD/home HD were also included in the fully adjusted models. All analyses were performed using SAS, version 9.4 (SAS Institute Inc.).
Sensitivity Analyses
To test the robustness of our findings, a sensitivity analysis was performed to impute race (missing in 8%) for patients where it was unknown. Race was imputed five times using a fully conditional specification method. The multiple imputation analysis results were combined to generate valid statistics (19). Furthermore, another sensitivity analysis was performed using a minimum treatment duration threshold of 90 days to define the primary outcome of having been treated with a home dialysis modality (PD or home HD).
Results
Baseline Characteristics
A total of 66,600 patients on incident chronic dialysis were registered in the CORR between 1996 and 2012. Race information was available for 61,237 (92%) patients. The majority of the cohort was white (75%), with other minorities represented as follows: Asian (7%), black (3%), Aboriginal (6%), Indian subcontinent (5%), and other (4%). Table 1 describes the baseline characteristics of the study population stratified by race. In-center HD as an initial dialysis modality was highest among Aboriginals (84%) and lowest among Asians (69%). Compared with whites, Asians were more likely to have GN as a cause of ESRD and had fewer comorbid illnesses. Conversely, black, Aboriginal, and Indian subcontinent patients were more likely to have diabetic kidney disease. Furthermore, Aboriginals had a higher prevalence of peripheral vascular disease, smoking, and obesity. Late referral was also more prevalent among Aboriginals. In regards to socioeconomic status, lower income quintiles were more common among black and Aboriginal patients. The characteristics of patients with unknown race are presented in Supplemental Table 1.
Baseline characteristics at dialysis initiation stratified by race in Canada, 1996–2012
Racial Differences in Home Dialysis Utilization
Baseline characteristics stratified by race in patients treated with PD, home HD, or in-center HD are summarized in Tables 2–4⇓⇓, respectively. Among patients treated with PD or home HD, Asians had a higher proportion of GN as the cause of ESRD and fewer comorbidities. However, diabetes was the predominant cause of ESRD among black, Aboriginal, and Indian subcontinent patients. Again, Aboriginals had more comorbid disease and were more likely to be referred late to a nephrologist. Income was equally lower among blacks and Aboriginals.
Baseline characteristics stratified by race of patients treated with peritoneal dialysis
Baseline characteristics stratified by race of patients treated with home hemodialysis
Baseline characteristics stratified by race of patients treated with in-center hemodialysis
The association between race and treatment with home dialysis varied among different racial groups (Figure 1). When treatments with HD and PD were examined together, treatment with a home dialysis modality was significantly lower only in Aboriginals compared with whites (adjusted relative risk [RR], 0.71; 95% confidence interval [95% CI], 0.66 to 0.76). It was higher in Asians (adjusted RR, 1.28; 95% CI, 1.22 to 1.35) and others (adjusted RR, 1.12; 95% CI, 1.04 to 1.20). No significant racial differences were seen among blacks or subcontinent Indians.
Association between race and treatment with home dialysis. Unadjusted and adjusted relative risks to be treated with (A) peritoneal dialysis, (B) home hemodialysis, and (C) any home modality. Reference: whites. Fully adjusted model: adjusted for age, sex, body mass index, cause of ESRD, comorbidity conditions, distance from dialysis center, facility size, income quintile, region within Canada, and era. 95% CI, 95% confidence interval.
For treatment with PD, the adjusted RRs were higher among Asians (RR, 1.31; 95% CI, 1.25 to 1.39) and others (RR, 1.13; 95% CI, 1.06 to 1.23) but significantly lower in Aboriginals (RR, 0.71; 95% CI, 0.67 to 0.76). There was no significant association between race and treatment with PD among blacks and subcontinent Indians. For treatment with home HD, Aboriginals (adjusted RR, 0.36; 95% CI, 0.27 to 0.48) and subcontinent Indians (adjusted RR, 0.73; 95% CI, 0.58 to 0.93) were less likely to be treated with this modality compared with whites, whereas no significant differences were seen among Asians, blacks, and other groups. Detailed regression models are presented in Supplemental Table 2.
Racial Differences in Risk of Technique Failure
Over the follow-up period, 6469 (33%) patients on PD and 502 (26%) patients on home HD developed technique failure. Median follow-up was 561 days (interquartile range, 238–1064) for patients treated with PD and 577 days (interquartile range, 222–1127) for patients treated with home HD. Unadjusted and adjusted hazard ratios (HRs) for technique failure, mortality, and the composite outcome of both stratified by race are presented in Figure 2 and Supplemental Table 3.
Association between race and clinical outcomes among home dialysis patients. (A) Association between race and technique failure in peritoneal dialysis. (B) Association between race and mortality in peritoneal dialysis. (C) Association between race and the composite outcome of technique failure and death in peritoneal dialysis. (D) Association between race and technique failure in home hemodialysis. (E) Association between race and mortality in home hemodialysis. (F) Association between race and the composite outcome of technique failure and death in home hemodialysis. Reference: whites. Fully adjusted model: adjusted for age, sex, body mass index, cause of ESRD, comorbidity conditions, distance from dialysis center, facility size, income quintile, region within Canada, era, type of peritoneal dialysis/home hemodialysis, and timing of starting peritoneal dialysis/home hemodialysis. 95% CI, 95% confidence interval.
Among patients on PD, black and Aboriginal patients had significantly higher adjusted hazards for technique failure compared with whites (adjusted HR, 1.31; 95% CI, 1.16 to 1.48 and adjusted HR, 1.19; 95% CI, 1.06 to 1.33, respectively). Conversely, Asians had a lower risk (adjusted HR, 0.89; 95% CI, 0.82 to 0.99). No significant differences were seen among subcontinent Indians or other racial groups. Among patients on home HD, no significant differences were seen in risk of technique failure among racial groups.
Racial Differences in Mortality Risk
In total, 6076 (31%) patients on PD and 277 (14%) patients on home HD died during follow-up. Among patients treated with PD, the adjusted risk of death was significantly lower in Asians, blacks, and others (adjusted HR, 0.83; 95% CI, 0.75 to 0.92; HR, 0.71; 95% CI, 0.59 to 0.85; and HR, 0.79; 95% CI, 0.68 to 0.92, respectively) but greater in Aboriginals (adjusted HR, 1.16; 95% CI, 1.02 to 1.32) compared with whites. In contrast to patients on PD, there were no significant differences in mortality across different racial groups treated with home HD (Figure 2, Supplemental Table 3).
Racial Differences in the Composite Outcome of Technique Failure and Death
The composite outcome of technique failure and death was also examined (Figure 2, Supplemental Table 3). Compared with whites, the adjusted risk of the composite outcome was significantly higher in Aboriginals, lower in Asians, and similar for other racial groups treated with PD. Conversely, in patients treated with home HD, the only significant difference in regard to the composite outcome was among Aboriginals, who had a higher adjusted risk.
Sensitivity Analyses
Adjusted imputed RRs for treatment with PD, home HD, and home dialysis were very similar to standard adjusted RRs (Supplemental Table 2). Similarly, adjusted imputed HRs for technique failure, death, and the composite outcome of technique failure and death were also very comparable with standard adjusted results (Supplemental Table 3).
Additionally, when a minimum treatment duration threshold of 90 days was used to define the primary outcome of having been treated with a home dialysis modality, results were also very similar to the primary analysis in regard to the primary and secondary outcomes (Supplemental Tables 4 and 5).
Discussion
In this Canadian national registry–based observational cohort study, we observed significant differences in home dialysis modality uptake and clinical outcomes on the basis of race. All nonwhite races, except for Aboriginals, were as or more likely to be treated with home dialysis. In fact, Asians were more likely to be treated with home dialysis, whereas no significant racial differences were found among blacks or subcontinent Indians in home dialysis utilization. Conversely, Aboriginal patients were significantly less likely to receive either home HD or PD. Furthermore, the risk of technique failure and death also varied considerably across races. Among patients on PD, black and Aboriginal patients had a higher adjusted risk of technique failure, whereas Asians had a lower risk compared with whites. The risk of death was significantly lower in Asians and blacks but higher in Aboriginals compared with whites in patients treated with PD. Among patients on home HD, no significant racial differences were seen in risk of mortality or technique failure. Taken together, nonwhite races, except Aboriginals, in Canada seem to have similar access to home dialysis as whites but differing clinical outcomes.
In contrast to the recent study by Mehrotra et al. (6) that showed that all racial groups in the United States were less likely to be treated with home dialysis compared with whites, treatment with home dialysis was lower only among Aboriginals in our Canadian cohort. This is likely partly due to geographic isolation, with more difficult access to predialysis care, education, and home dialysis facilities. Furthermore, regional resources to support home dialysis may be limited in addition to an increased burden of illness and a higher prevalence of diabetic kidney disease and vascular comorbidities: factors associated with lower home dialysis use (20,21). Conversely, Asians and others were more likely to be treated with a home dialysis modality, which may perhaps be accounted for by lower comorbid disease and higher occurrence of GN as the cause for ESRD. The absence of any major racial differences in home dialysis use may be potentially explained by our universal government-funded health care system, improved access to predialysis education, and possibly, more home dialysis experience in treating physicians given the higher overall home dialysis utilization in Canada (15). In fact, previous studies have shown that nonwhite races have lower access to pre-ESRD care in the United States, which may contribute to disparities in home dialysis utilization (22). It is possible that, despite potential racial differences in socioeconomic status, public health care delivery ensures that access to home dialysis is more equitable.
Nonetheless, comparable with the recent United States analysis (6), our study equally showed that, among patients on PD, blacks had a higher risk of transfer to in-center HD, whereas the risk was lower in Asians compared with whites. Previous studies have shown higher rates of peritonitis among blacks in Canada, which may contribute to the increased risk of technique failure (23). Whether increased risk of peritonitis is related to biologic differences or socioeconomic factors is unknown. It is important to emphasize that both social and medical factors play a role in technique failure (24). With the use of a large national administrative dataset, it was not possible to discern these potential social factors.
Similarly, the observation of a lower mortality risk in Asians, blacks, and others treated with PD compared with whites is also consistent with previous reports (6,11,25,26). Indeed, in Hong Kong, where a PD first policy exists, excellent patient and technique failure have been described (27). Different degrees of comorbid illness are insufficient to explain this paradoxical survival advantage. Previous studies have postulated that racial minorities have lower transplantation rates, which may confer a survivor bias (6,28). However, by using a competing risk model, we did account for potential different kidney transplantation rates across racial groups. Other proposed mechanisms have implicated genetic or biologic differences, improved inflammatory profiles, better nutritional status, differences in physical activity, and other socioeconomic factors (29,30).
The findings of lower home dialysis utilization in Aboriginal patients, with higher rates of technique failure and mortality among those treated with PD, are also consistent with prior studies (31,32). Similar to blacks, higher rates of peritonitis have also been reported among Aboriginal patients (32–34). Likewise, in Australia, mortality rates are significantly higher in Aboriginal patients compared with nonindigenous patients for all renal replacement modalities, even after adjustment for comorbidities (35). Despite universal health care, these Aboriginal-white disparities are likely explained by greater comorbid disease with higher cardiovascular risk, socioeconomic disadvantage, geographic isolation, and significant limitations to access to care in rural areas. Indeed, socioeconomic inequalities are well described among Aboriginals in Canada, with average income <75% of that among non-Aboriginals and lower employment status (36). This may partly be explained by lower education level given significantly higher high school dropout rates and fewer employment opportunities due to geographic location (37).
Our results are also similar with studies in the general population, which have shown that the extent and patterns of racial differences seem to vary across cohorts (38). More recently, Ramraj et al. (38) showed that black-white and Hispanic-white racial disparities predominated in the United States, whereas Aboriginal-white disparities were more significant in Canada in regards to health outcomes. Thus, the relationship between race and health seems to depend on the sociocultural setting. Nonetheless, despite universal health care, studies have shown that racial differences still exist in access to care in Canada, although these differences are significantly less marked than those in the United States (39). In fact, nonwhites are slightly less likely to have a regular doctor and less likely to be treated for psychiatric illness and receive certain screening tests (39). Similar to the results of our study, there are also important racial differences in mortality in the general population in Canada. Mortality rates have been shown to be higher among Aboriginals but substantially lower among other nonwhites. However, this mortality benefit is attenuated as the number of years since immigration increased, often referred to as a healthy immigrant effect (40). Moreover, the black population in Canada may be very different from the United States black population. In fact, although there is a large proportion of recent immigrants among blacks in Canada, blacks in the United States are more likely to be longstanding residents and descendants of a population exposed to discrimination (38,41). Important socioeconomic differences among the black populations also exist between Canada and the United States. In fact, compared with the United States, blacks in Canada had relatively higher education, income, and employment (42). Nonetheless, recent studies have shown that black-white disparities still persist in Canada in regards to income and education (43,44).
This study needs to be interpreted on the context of the study design, and several limitations should be noted. The use of a large administrative dataset is subject to limitations arising from data validity and missing data elements. In fact, absence of validation of race could have led to misclassification. Moreover, racial data were missing in 8% of patients. This was partially accounted for by performing a multiple imputation analysis, which did not change our primary results. However, it is possible that race was more likely to be missing among certain racial groups compared with others. Nonetheless, comorbid conditions reported in the CORR have been validated and as a result, likely provide reliable information (17). Additionally, the relatively small number of patients treated with home HD (n=1906) could have limited the power to detect significant findings in this subgroup, especially in regards to the absence of significant racial differences in clinical outcomes. Information regarding language, immigration status, and center-specific experience with home dialysis was not available and could have resulted in residual confounding. Furthermore, data on the circumstances under which patients initiated dialysis were not available and may have been informative. However, late referral, initial treatment with in-center HD, and central venous catheter use may be proxies for the acuity of dialysis initiation in our cohort. Indeed, all of these factors were more frequent among Aboriginal patients compared with other racial groups. Lastly, data from the province of Quebec were not included because of the need for additional ethics and data permissions. Because Quebec is home to a large multicultural population, the exclusion of data from this province is an important limitation. Notwithstanding these limitations, our major study strength was the use of a large multicenter cohort of patients on home dialysis, with extensive adjustment for comorbid conditions and long follow-up. This study has comprehensively examined racial differences in home dialysis utilization and clinical outcomes in a large national cohort in the setting of a universal government-funded health care system. Except for Aboriginals, nonwhite races in Canada were not less likely to be treated with home dialysis. This contrasting finding may be the result of a more equitable access to home dialysis within a public health care system in addition to more adequate pre-ESRD education. However, similar to other studies, we found significant differences in the clinical outcomes of mortality and technique failure among patients on PD. With resurgence of interest in home dialysis modalities, it is imperative to better understand racial differences in home dialysis outcomes, particularly among black and Aboriginal patients. Future research should focus on better understanding technique failure, with potential interventions that could be implemented to improve the sustainability and outcomes of home dialysis.
Disclosures
M.M.S. holds the Jindal Research Chair in the Prevention of Kidney Disease at the University of Ottawa and has received investigator-initiated grant funding from Otsuka. C.T.C. holds the R. Fraser Elliot Chair in Home Dialysis and consulted for Baxter Inc., NxStage Inc., and Intelomed Inc. J.P. has received speaking honoraria from Baxter Healthcare and consulting fees from Baxter Healthcare, Fresenius Medical Care, Otsuka, Janssen Ortho Shire, Takeda, and Boehringer–Ingelheim as well as research support from Baxter Healthcare and salary support from Arbor Research Collaborative for Health.
Acknowledgments
The authors acknowledge the staff at the Canadian Organ Replacement Register (CORR) for maintaining the database and the dialysis facilities throughout Canada for submitting information to the CORR. No financial support was received.
Footnotes
Published online ahead of print. Publication date available at www.cjasn.org.
This article contains supplemental material online at http://cjasn.asnjournals.org/lookup/suppl/doi:10.2215/CJN.03820417/-/DCSupplemental.
- Received April 7, 2017.
- Accepted July 17, 2017.
- Copyright © 2017 by the American Society of Nephrology