We documented the higher prevalence of comorbidities, including hypertension, cerebrovascular disease, lower-extremity amputations, mental health disorders, and liver disease, among American Indian adults with diabetes living in central Arizona compared with those of a sample of commercially insured U.S. adults with diabetes. These comorbidities not only complicate diabetes treatment and influence a individual's ability to manage his or her own diabetes but are also associated with lower quality of life and higher mortality.
The morbidity burden among the American Indian with diabetes exceeded that of the U.S. adults with diabetes by 50%. Accordingly, American Indian adults with diabetes in this study would be expected to use 50% more health resources than U.S. adults with diabetes and commercial insurance. The magnitude of increased risk among American Indians with diabetes remained fairly constant across all ages. Using the 2005 MarketScan health expenditure for an adult with average risk ($3,050), a U.S. adult with diabetes was estimated to cost ~$12,800 during 2005 and an American Indian adult with diabetes ~$19,260. The IHS was the primary provider of medical services for the American Indian adults included in this study. Service delivery and treatment costs within the IHS differ from services accessed in the private sector. Consequently, MarketScan health expenditure estimates are not directly comparable to IHS health expenditures. However, the findings concerning the exceedingly higher risk of American Indian adults with diabetes may be used to evaluate the financial resources available to meet treatment needs of American Indians with diabetes.
Furthermore, the findings may be used to inform efforts to enhance prevention and treatment programs, particularly programs to prevent complications among American Indians with diabetes. The findings document the need for strong linkages between behavioral and physical health providers for younger adults with diabetes. CVD was prevalent among American Indian and U.S. adults with diabetes, yet the morbidity burden among American Indian adults with both diabetes and CVD was ~40% higher than that of U.S. adults with both conditions. Given the high rates of premature death from heart disease among American Indians and Alaska Natives, the specific treatment needs of these patients should be explored. Finally, DCG risk scores may be used to target interventions for those with extremely high risk to reduce the likelihood of additional complications associated with diabetes.
This is the first study to compare the prevalence of several comorbidities and the overall morbidity burden of American Indian adults with diabetes with those for commercially insured U.S. adults with diabetes, controlling for age differences. However, it is important to note several limitations. First, the study included data for only IHS active users. Still, they represent a very large proportion of individuals eligible for IHS services in the Service Unit (25
). Second, we analyzed American Indian data for services obtained at non-IHS facilities if IHS provided payment for the services through Contract Health Services. Consequently, we did not have data with the diagnostic codes for services not reimbursed by IHS. This may have biased downward the prevalence rates of diabetes and other conditions (e.g., heart disease) reported for American Indian adults in this study.
Third, we chose a U.S. adult population with commercial health insurance as our comparison population. Although the prevalence of diabetes among the MarketScan adult sample was similar to the estimated prevalence among U.S. adults aged 18–64 years (7
), we recognize that the average household income of commercially insured U.S. adults exceeded that of the American Indian population, who may have had an average household income closer to that of Medicaid and uninsured populations. Adults with lower incomes and nonmajority ethnic and racial backgrounds are often less likely to use medical services for several reasons including financial and geographic access, culture, and discrimination. MarketScan does not include data for individuals with Medicaid or Medicare coverage or uninsured individuals. We did not consider using a Medicaid population as a comparison population because the age and sex distributions of adult Medicaid populations, which are driven by eligibility categories, differ from those of the American Indian adults. With limited financial access to medical services, the diagnostic codes recorded in claims data for uninsured individuals may underestimate their disease burden. We believe the diagnostic codes recorded in the MarketScan data are a reasonable indicator of the health status of the commercially insured U.S. study population. The differences between the American Indian and the U.S. adults observed in this study are undoubtedly larger than would be differences between American Indians and a representative U.S. population that included adults with lower incomes and in poorer health than the commercially insured adults. We were unable to identify data for a representative U.S. sample that is comparable to the IHS data. We concluded that the strengths of the MarketScan data (e.g., a large sample that allowed for a study of comorbidities among individuals with diabetes and the ability to use DCG models to identify comorbidities and to quantify the morbidity burden) far exceeded the limitations inherent in its use.
Fourth, we extracted data for somewhat different time periods for the American Indian adults (FY 2005) and U.S. adults (calendar year 2005). We believe this difference had minimal impact on the findings. For both study populations, prevalence rates were based on administrative data for one 12-month period and most likely underestimated actual prevalence rates. Finally, this study provides important information concerning morbidity for nearly 2,800 American Indian adults in central Arizona with diabetes. However, there are >550 federally recognized tribes throughout the U.S. and tribal variations in culture, traditions, history, and the prevalence of diabetes are well documented (5
). For example, the diabetes prevalence among all American Indian adults in the Phoenix Service Unit, including those with Medicare coverage and aged ≥65 years, was 10.9% during FY 2005, a rate that is consistent with previous IHS estimates. During 2004, the prevalence among American Indians and Alaska Natives aged ≥20 years was <10% in Alaska and >20% in North Dakota (5
). Consequently, these results may not be generalizable to other American Indian and Alaska Native populations and additional studies are needed.
The morbidity burden among American Indians with diabetes far exceeded that of commercially insured U.S. adults with diabetes. The information concerning the prevalence of comorbidities among American Indians with diabetes may inform government and tribal efforts to enhance diabetes prevention and treatment and ultimately reduce disparities between American Indian and U.S. populations in diabetes-related morbidity and premature mortality.