Our results suggest that there are differences in the care received by status Aboriginal and non-Aboriginal people with chronic kidney disease. First, Aboriginal people with chronic kidney disease do access the health care system, as shown by the use of general practitioner and emergency department services. However, Aboriginal people with chronic kidney disease were almost twice as likely as non-Aboriginal people to be admitted to hospital for an ambulatory-care–sensitive condition related to their chronic kidney disease. In addition, despite national guidelines recommending that people with severe chronic kidney disease visit a nephrologist, we found that Aboriginal people with severe chronic kidney disease were significantly less likely than non-Aboriginal people to have visited a nephrologist.
Although universal coverage for health care in Canada has alleviated insurance-related barriers to care,30
our results suggest that other barriers may exist among Aboriginal people, who are less likely than non-Aboriginal people to receive specialized care for chronic kidney disease. This is unlikely to be related to lack of access to the health care system in general, because almost all Aboriginal people in our study had at least 1 visit to a general practitioner. The probability of obtaining a serum creatinine measurement is also unlikely to have influenced these results, as we have reported that Aboriginal people have an increased likelihood of having a serum creatinine measurement compared with non-Aboriginal people.31
Decreased access to specialized medical care among Aboriginal people has been reported.14,15
Potential barriers, including distance from specialized care, require further study. Delayed referral to a nephrologist for severe chronic kidney disease is not unique to the Aboriginal population and has been reported in other ethnic groups.32,33
Given the increased mortality among patients with a late referral to a nephrologist,12,34,35
these results suggest suboptimal quality of care in the Aboriginal population and the need for interventions to reduce or eliminate these disparities.
Access to health care is difficult to evaluate, and ambulatory-care–sensitive conditions are commonly used as a measure of access and assessment of performance of the health care system.16,17
Barriers in access are complex and include patient, environmental and health system factors. Lower socio-economic status has been associated with an increased likelihood of hospital admission for an ambulatory-care–sensitive condition in the United States16
and an increased frequency of physician visits in Canada.30
However, even after adjustment for median household income and rural location of residence, Aboriginal people were still 50% more likely than non-Aboriginal people to be admitted to hospital for an ambulatory-care–sensitive condition related to their chronic kidney disease. Controlling for socio-economic status and location of residence may result in over-adjustment because these factors are considered to be a component of ethnicity29
and may artificially reduce differences in rates hospital admissions for ambulatory-care–sensitive conditions. Thus, in our main analysis, we did not adjust for median household income and rural location of residence. We found a similar increased risk for all-cause hospital admissions among status Aboriginal and non-Aboriginal people (Appendix 3, available at www.cmaj.ca/cgi/content/full/179/10/1007/DC2
), which suggests that the increased risk extends beyond ambulatory-care–sensitive conditions related to chronic kidney disease. However, with the present data, we are unable to determine the extent to which patient factors such as compliance with recommended treatments, including attendance at physician appointments, may have influenced the study results.
Although we did not have access to the details of the medical care provided to Aboriginal people with chronic kidney disease, lack of access to specialized care may result in suboptimal use of treatments that reduce the risk of progression of kidney disease,9,10
and may contribute to higher rates of end-stage renal disease in this population. This is further supported by our previous study that showed a lower prevalence of all stages of chronic kidney disease but a higher prevalence of more severe chronic kidney disease and increased mortality rates among status Aboriginal people than among non-Aboriginal people.31
Our study had several limitations. First, we did not directly calibrate serum creatinine measurements to measurements made at the Cleveland Clinic, where the Modification of Diet in Renal Disease equation for estimated glomerular filtration rate was derived. We did, however, implement a province-wide standardization of serum creatinine measurements that had been indirectly calibrated to the isotope dilution mass spectrometry reference standard using the new Modification of Diet in Renal Disease equation.28
Second, we were not able to identify Metis people and non-registered Aboriginal people, which may have resulted in misclassification of some Aboriginal patients as non-Aboriginal. However, given that the majority of the Aboriginal population in Alberta is registered under the federal Indian Act and given the size of the non-Aboriginal population, this potential misclassification would have had minimal impact on our results, and if there was a bias, it would have been toward the null hypothesis. Third, use of laboratory data to define the cohort limited our study to patients who had sought medical care and who had a serum creatinine measurement, which may limit the generalizability of our results. Finally, as with all observational studies, the possibility of residual confounding cannot be excluded. Although we were unable to directly adjust for patient-related factors such as compliance and distance to the nearest nephrologist, we were able to account for key clinical variables, including diabetes and baseline kidney function. The hazard ratios associated with ethnic background and likelihood of a nephrologist visit were substantial, and they are unlikely to be completely negated by adjustment for additional covariables.
The results of our study suggest potential inequities in care between status Aboriginal people and non-Aboriginal people with chronic kidney disease. The extent to which these inequities may contribute to the higher rates of end-stage kidney failure among the Aboriginal population requires further exploration. Interventions that target these disparities in care are needed.
@@ See related commentary by Peiris and colleagues, page 985