Racial Differences in Diabetic Nephropathy, Cardiovascular Disease, and Mortality in a National Population of Veterans

BESSIE A. YOUNG 0 CHARLES MAYNARD 0 PHD 0 EDWARD J. BOYKO 0 0 Young , Maynard, and Boyko OBJECTIVE - To determine racial differences in the prevalence of diabetic nephropathy, cardiovascular disease (CVD), and risk of mortality in a national health care system. RESEARCH DESIGN AND METHODS - A longitudinal cohort study was conducted in 429,918 veterans with diabetes. Racial minority groups were analyzed for baseline differences in prevalence of early diabetic nephropathy, diabetic end-stage renal disease (ESRD) and CVD, and longitudinal risk of mortality compared with Caucasians. RESULTS - The 429,918 patients identified with diabetes were of the following racial groups: Caucasian (56.2%), African American (15.3%), Asian (0.5%), Native American (0.4%), and unknown race (21.4%). Minority individuals were, on average, younger and less likely to have CVD but were more likely to have renal disease than Caucasians. After adjustment for age, sex, and economic status, African Americans (adjusted odds ratio [OR] 1.3, 95% CI 1.2-1.4) and Native Americans (1.5, 1.1-2.1) were more likely to have early diabetic nephropathy than Caucasians. Diabetic ESRD was more likely to be present in African Americans (1.9, 1.9 -2.0), Hispanics (1.4, 1.3-1.4), Asians (1.8, 1.5-2.1), and Native Americans (1.9, 1.5-2.3) than Caucasians. Concurrently, the adjusted OR of CVD in racial minority groups was 27- 49% less than in Caucasians, whereas the 18-month risk of mortality among people from most racial minority groups was 7-12% lower than in Caucasians. CONCLUSIONS - We conclude that when access to care is comparable, microvascular complications, macrovascular disease, and subsequent death occur with different frequencies among various racial groups. - D care problem that is estimated to af- affects 20 40% of individuals with diaiabetes is a substantial public health they have the disease (1,2). Renal disease fect over 16 million Americans, ap- betes (35), and diabetic nephropathy is proximately half of whom are aware that the leading cause of end-stage renal dis ease (ESRD) or dialysis dependence in the U.S. (6). Compared with Caucasians, racial minority populations are disproportionately affected by diabetes (7,8) and have excessive risk for such complications as ESRD (9) and amputations (10,11). The Multiple Risk Factor Intervention Trial (MRFIT) (12) found that African Americans had a higher risk of diabetic ESRD than Caucasians, whereas Pugh et al. (13) described an excess incidence of diabetic ESRD in African Americans and Hispanics, a finding that was confirmed more recently in the U.S. Renal Data System (USRDS) (9). Small population studies of diabetes and its complications have been conducted in the U.S., the primary focus of which has been homogeneous groups of patients such as Caucasians in the Midwest (5,14,15) or Pima Indians in the Southwest (12,16 26). Recently, Karter et al. (11) found that among Kaiser Permanente enrollees, African Americans and Hispanics had a higher prevalence of ESRD than Caucasians but lower or similar prevalence of other diabetes complications. However, overall survival and prevalence of non-ESRD conditions were not determined. Other studies have evaluated racial differences in the prevalence and incidence of ESRD (12,16 18), but few data describe racial differences in renal disease and other complications before initiation of dialysis. We and others have shown that certain microvascular complications occur more frequently in some racial minority groups (10,11), and others have shown that macrovascular complications such as cardiovascular disease (CVD) occur more frequently in Caucasians than in racial minorities (11). Therefore, we hypothesized that in a setting in which access to care is comparable, African Americans and other racial minorities are more likely to develop microvascular complications, such as renal disease, whereas Caucasians, are more likely to develop macrovascular complications, such as CVD, and that these differences may account for the variation in mortality when access to care is similar. Using administrative databases, this study investigated racial differences in the risk of early diabetic nephropathy, diabetic ESRD, CVD, and mortality in a national setting among veterans where access to health care was comparable among enrollees. RESEARCH DESIGN AND METHODS Subjects and settings We conducted a longitudinal cohort study of subjects with diabetes who received care nationally within the Department of Veterans Affairs (VA) as described previously (10). Inclusion in the study required a diagnosis of diabetes during fiscal year 1998 and three subsequent clinic visits within 1 year. Data were extracted from 1 October 1997 until death or 31 March 1999. Diabetic subjects were identified through the national Veterans Health Administration (VHA) databases at the Austin Automation Center (Austin, Texas) by the presence of at least one outpatient visit with an ICD-9 (27) diagnosis code of diabetes (250.XX) during fiscal year 1998. Data were extracted from both inpatient (Patient Treatment Files) and outpatient files (Outpatient Care Files by use of ICD-9 codes and Common Procedural Terminology codes) (28) (see online appendix at http:// care.diabetesjournals.org). Patient Treatment Files and Outpatient Care Files were merged and duplicate listings were eliminated before analyses. No distinction was made between those with type 1 or type 2 diabetes. Exposures Potential risk factors for renal disease were identified a priori and included race, age at beginning of study, sex, and service connection for medical services received. In VA records, race or national origin is extracted from clinical documentation and/or observation of administrative staff and does not take self-report into account. The term racial minority will therefore be used to define ethnic minority groups or non-Caucasians for the remainder of this study. Service connection has been used as a proxy for socioeconomic status in the VA setting (10). VA criteria for health care eligibility include a service-connected disability or low financial resources; absence of a serviceconnected disability is therefore an indicator for low socioeconomic status. Comorbid conditions such as hypertension, stroke, cancer, chronic obstructive pulmonary disease (COPD), and depression were identified by use of ICD-9 codes and were included as potential exposure covariates. Because data on smoking history were not available, a prevalent diagnosis of COPD was used as a proxy for significant smoking history (29). Other extracted covariates of interest included geographic region, diagnosis of diabetic eye disease, total number of clinic visits, and number of hospitalizations. Outcomes Diabetic nephropathy was defined by the ICD-9 code 250.4 or the code for diabetes (250.XX) coupled with codes for additional secondary renal conditions such as glom (...truncated)