© 2003 by the American Diabetes Association, Inc.
Prevalence of Diagnosed Diabetes Among African-American and Non-Hispanic White Youth, 1999
1 Department of Epidemiology and Biostatistics, Arnold School of Public Health, University of South Carolina, Columbia, South Carolina Address correspondence and reprint requests to John Oeltmann, Arnold School of Public Health, University of South Carolina, 2718 Middleburg Dr., 2nd Floor, Columbia, SC 29204. E-mail: je03{at}cdc.gov
OBJECTIVETo document diabetes prevalence among African-American and non-Hispanic white youth in a two-county region in South Carolina. RESEARCH DESIGN AND METHODSWe conducted a population-based surveillance effort to identify case subjects aged 018.9 years with a physician diagnosis of diabetes residing in a two-county region in 1999. Case subjects were ascertained from hospitals, the sole office of pediatric endocrinology, and several smaller sources. Case subjects were classified according to the diagnosis made by a pediatric endocrinologist. As a completeness check, eight randomly selected physicians were queried for eligible case subjects. Capture-recapture provided an additional measure of completeness. Prevalence estimates used U.S. 2000 Census data for the two-county denominator. RESULTSCrude total diabetes prevalence was 1.7 cases per 1,000 youth and similar between African-American and non-Hispanic white youth. Among younger youth (09.9 years), non-Hispanic white total prevalence was 1.1 per 1,000 and African-American prevalence was 0.6 per 1,000. Among older youth (10.018.9 years), non-Hispanic white total prevalence was 2.5 per 1,000 and African-American prevalence was 3.1 per 1,000. Type 2 diabetes was only confirmed among older prevalent cases. Ascertainment completeness was estimated to be 98%. CONCLUSIONSOur estimates suggest that total diabetes prevalence among non-Hispanic white youth is similar to rates observed over 20 years ago. Among African-American youth, the difference in prevalence noted between younger and older age-groups was notably greater than that observed among the non-Hispanic white youth, potentially reflecting a more marked increase in diabetes incidence with age.
Abbreviations: ADA, American Diabetes Association RLDR, Richland/Lexington County Childhood and Adolescent Diabetes Registry
The emergence of type 2 diabetes among youth in North America has recently been described (1). Population-based data suggest that the incidence of type 2 diabetes among older African-American and non-Hispanic white youth is increasing (2), and several studies conducted within specialty clinics have noted increasing numbers of youth diagnosed with type 2 diabetes (1,3). Additionally, indications of an increase in the incidence of type 1 diabetes have been reported among nonwhite children in the U.S. (4). However, we know very little about how these increases have affected the overall population burden or prevalence of diabetes in youth. There are no prevalence estimates for type 2 diabetes among youth with the exception of Native American populations (56), nor are there any recent estimates of prevalence of type 1 diabetes in the U.S. According to data collected primarily among non-Hispanic white youth before the mid-1980s, the median prevalence of type 1 diabetes was 1.7 cases per 1,000 youth (7). The lack of standard case definitions for type of diabetes in youth, differing case ascertainment methodologies, and the recent widespread awareness of type 2 diabetes among youth make comparisons of previously recorded prevalence estimates of childhood and adolescent diabetes very difficult. Currently it is not entirely clear whether the apparent increasingly frequent reports of type 2 diabetes among youth reflect true increases in incidence, the result of changing diagnosis patterns due to increasing physician awareness, increased screening, or some combination thereof. Until accurate case definitions for type 1 and type 2 diabetes can be applied to population-based surveillance efforts, type-specific prevalence estimates will be difficult to establish. Because both type 1 and type 2 diabetes can result in similar diabetes-related complications later in life, this study focused on overall diabetes burden in youth and considered type-specific estimation as a secondary aim. This study will help describe the burden of diabetes among non-Hispanic white and African-American youth.
The Richland/Lexington County Childhood and Adolescent Diabetes Registry (RLDR) was a population-based effort that identified youth who had a physician diagnosis of diabetes, were a resident of Richland or Lexington county, and were aged <19 years (born on or after 1 January 1981, for the index year of 1999).
Case identification
Case validation
Typology
Denominator
Estimation of prevalence
Completeness of case ascertainment Second, multiple-source capture-recapture methods using the log-linear approach described by Hook and Regal (11) were used to estimate the true number of cases within the two-county region. Three analytical sources were defined to adjust for potential dependencies between sources and include the pediatric endocrinologist, all participating hospitals (combined as one source), and the remaining sources (combined as one source). Capture-recapture estimates were calculated by race and for the entire population. The randomly selected physicians were not included in the capture-recapture analysis, as they were considered an independent means to assess completeness of ascertainment.
Initially 368 unique individuals were reported to the RLDR. Of these reports, 245 were eligible and valid diabetic case subjects, 71 were false-positive reports (validated as never diagnosed with diabetes), 8 were found ineligible due to moving from the catchment area, 2 were found to have diabetes secondary to another condition, and 1 had died before 1999. The remaining 41 reports were excluded because diabetes status could not be validated, even after medical record review. The large number of false-positive reports was largely the result of using billing data as an initial means to identify potential case subjects.
Total diabetes prevalence
Proportion of youth with type 1, type 2, and unknown diabetes type Among those seen by a pediatric endocrinologist (n = 181) and therefore assigned diabetes type, 152 were classified as type 1 diabetic case subjects and 29 were classified as type 2 diabetic case subjects. Within every race, sex, and age subgroup we identified and validated case subjects that had not been seen by the pediatric endocrinologist and therefore remained of unknown type for this study. Figures 1 and 2 show proportions of youth with type 1, type 2, and unknown diabetes type among youth with diagnosed diabetes.
Among those aged <10 years, 14 of 64 case subjects were not assigned a specific diabetes type (Fig. 1). Proportions of youth with undetermined diabetes type ranged from 8% (non-Hispanic white males) to 40% (African-American males). Among the others, we found no prevalent cases of diagnosed type 2 diabetes. However, four individuals who were aged >10 years and currently classified as having type 2 diabetes were initially diagnosed with type 2 diabetes before their 10th birthday. Among the older youth, diabetes type was not assigned to 50 (28%) of the identified case subjects. Among those for whom type was assigned, older African-American females formed the largest proportion diagnosed with type 2 diabetes (Fig. 2). Approximately one-half (44.8%) of all older African-American females diagnosed with type 1 or type 2 diabetes were diagnosed with type 2 diabetes. The proportion was lower for African-American males, non-Hispanic white males, and non-Hispanic white females (19.2, 14.3, and 12.1%, respectively).
Case ascertainment completeness
Recent studies describe increasing numbers of youth classified as having type 2 diabetes (1,3). Most studies reporting on prevalence in the U.S. were conducted primarily among non-Hispanic white youth >20 years ago, when childhood diabetes was considered to be type 1 diabetes. Interestingly, total diabetes prevalence for all races in this study (1.7 cases per 1,000 youth) was similar to previously reported rates of type 1 diabetes among youth, which also cluster around 1.7 cases per 1,000 youth (7). Since there is no evidence of decreasing incidence of type 1 diabetes among the young, this could suggest that changing diagnostic patterns account for some of the increased numbers of youth diagnosed with type 2 diabetes. Alternatively, this may suggest that diagnosis of type 2 diabetes among the general population is still very rare relative to the existing number of cases of childhood type 1 diabetes and therefore has had little effect on the population prevalence of diabetes. However, further examination regarding specific diabetes type within age and race subgroups suggests that if type 2 diabetes among youth in our general population is epidemic, it appears to affect older African-American youth more often than their non-Hispanic white peers. Thus, our population-based findings are consistent with previous studies that found that nonwhite youth account for the majority of cases of type 2 diabetes (1). We found that type 2 diabetes accounts for 26% of prevalent African-American case subjects and only 10% of prevalent non-Hispanic white case subjects who were classified by type. Similar to findings from a nearby clinic-based study in coastal South Carolina in which almost one-half (46%) of African-American youth aged 1019 years with new-onset diabetes was classified as having type 2 diabetes (12), we found that almost one-half of the older African-American females with diagnosed type 1 or type 2 diabetes were classified as having type 2 diabetes. Two studies of prevalence conducted among school-aged youth in the 1970s suggested that prevalence rates of type 1 diabetes among non-Hispanic white youth were approximately twice as high as those noted among minority populations (1314). This is consistent with what we observed for total diabetes prevalence among youth aged <10 years, the age-group in which no prevalent cases of type 2 diabetes was noted. In contrast, among the older youth we found that total diabetes prevalence among African-American youth is now higher than that of non-Hispanic white youth. In Chicago, increasing incidence of childhood diabetes among minority youth is driven by an increase in youth with type 2 diabetes (15), which may explain the relatively high total diabetes prevalence among older African-American youth noted in this study. Currently there are no widely used case definitions for classifying diabetes type among youth. Although most youth diagnosed with type 2 diabetes are older at diagnosis, belong to a minority population, and are overweight or obese (1), these factors cannot be used to rule out type 1 diabetes. The ADA recommends classification based on pathogenic criteria (8). However, this recommendation is very difficult to apply to population-based efforts that focus on prevalence. We found that many youth, especially those diagnosed years ago, did not undergo a thorough pathophysiological evaluation and classification was therefore limited to clinical impression. Further complicating the estimation of type-specific rates are those case subjects whose clinical information is not readily available or unobtainable. This study suffered from the lack of laboratory data needed to better assign diabetes type for the entire cohort and the lack of clinical data for those who ultimately were classified as type unknown. The majority of children included in this study (73%) were assigned diabetes type by their pediatric endocrinologist according to clinical presentation and clinical course. According to the ADA Consensus Statement "Type 2 Diabetes in Children and Adolescents" (16), most cases can be accurately classified based on disease presentation and course; we therefore feel that misclassification of case subjects seen by the pediatric endocrinologist is minimal. The remaining 27% of case subjects were not current patients of the local pediatric endocrinologist; therefore, reliable and consistent data regarding diabetes type were not available. It is important to note that a larger percentage of non-Hispanic white youth were identified by the local pediatric endocrinologist than their African-American peers (80 and 66%, respectively), and therefore a greater proportion of African-American youth were not classified according to diabetes type. This was an unfortunate finding considering this is the population subgroup in which diabetes typology is perhaps most critical. To provide at least a tentative estimate of prevalence of type 2 diabetes among both African-American and non-Hispanic white youth, we applied the race/sex-specific proportion of case subjects diagnosed with type 2 diabetes (noted among the patients of the local pediatric endocrinologist) to those whose diabetes type is unknown. From this exercise we estimate the following number of cases of type 2 diabetes per 1,000 youth aged >10 years: 0.6 total, 0.4 non-Hispanic white males, 0.3 non-Hispanic white females, 0.5 African-American males, and 1.5 African-American females. Among all youth aged 018.9 years, prevalence of type 2 diabetes is estimated to be as low as 0.3 per 1,000. Assuming these estimates of type 2 diabetes are correct, we can estimate that the numbers of type 1 diabetes cases per 1,000 youth aged >10 years are: 2.0 total, 2.2 non-Hispanic white males, 2.4 non-Hispanic white females, 2.3 African-American males, and 1.9 African-American females. While type 2 diabetes among the young has received a great amount of attention recently, this study suggests that type 1 diabetes remains the much larger burden for both African-American and non-Hispanic white youth in our general population of youth <19 years of age. Regardless of specific diabetes type, overall rates presented here appear to be sound according to two completeness checks. Both suggest that RLDR approached completeness of ascertainment, thus strengthening our prevalence estimates. Several ascertainment biases were considered that could not be evaluated through capture-recapture analysis or the random selection of physician practices. Most importantly, this study describes prevalence of diagnosed diabetes, and no screening effort was undertaken to determine the amount of undiagnosed cases. Additionally, this study describes diagnosed case subjects that receive care. It is possible that some youth/young adults do not receive care regularly, therefore detection with our system would be unlikely. Finally, it is possible that eligible diagnosed case subjects travel outside of these two counties for care and would therefore remain undetected. However, the counties surrounding Richland and Lexington counties are extremely rural, and the nearest urban centers with large medical centers and endocrinology departments are between a 1- to 2-h drive away. While we cannot determine the number of patients who seek care exclusively outside Richland or Lexington counties, we do not feel that this led to severe underascertainment. The proportion of those diagnosed with type 2 diabetes has been shown to be increasing among those diagnosed with diabetes; however, data showing increasing prevalence or even increasing numbers of youth with diabetes of any type is sparse among African-American and non-Hispanic white populations. Although we were unsuccessful in estimating type-specific rates, this is to the best of our knowledge the first study to suggest that the overall burden or prevalence of diabetes is similar between African-American and non-Hispanic white youth aged 018.9 years. While crude rates are similar across race, perhaps the most important observation from this study is noted after stratification by age-group and race. Among African-American youth, the difference in prevalence noted between younger and older age-groups was notably greater than that observed among the non-Hispanic white youth, potentially reflecting a more marked increase in diabetes incidence with age. Estimation of type-specific rates presents epidemiologists with major challenges. While this study classified youth as having type 1, type 2, and unknown diabetes type, youth with clinical features of type 2 diabetes and metabolic features more typically seen in type 1 diabetic patients may further blur the lines of diabetes typology. As the prevalence of overweight youth in our nation continues to increase, particularly among non-Hispanic, African-American, and Mexican-American youth (17), a larger proportion of true type 1 diabetic patients will be overweight, presenting clinicians with even greater diagnostic challenges without the help of laboratory data. Complete understanding of the recently labeled epidemic will require multiracial population-based studies that consistently collect autoimmune markers and clinical characteristics at onset to assign diabetes type.
A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances. Received for publication February 12, 2003. Accepted for publication June 12, 2003.
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