- Email: [email protected]
Trends in Diabetes Mellitus Among Privately Insured Children, 1998–2002
Trends in Diabetes Mellitus Among Privately Insured Children, 1998 –2002 Alex R. Kemper, MD, MPH, MS; Kevin J. Dombkowski, DrPH; Ram K. Menon, MD, MBBS; Matthew M. Davis, MD, MAPP Objective.–To evaluate trends in health care administrative claims for childhood diabetes mellitus. Methods.–We conducted a serial cross-sectional study of a national sample of privately insured children ⱕ18 years old. The number of subjects ranged from 306 991 in 1998 to 974 407 in 2002. We classified diabetes type by 2 schemes: one based on encounter claims only, and the other based on both encounter and pharmacy claims. The prevalence of diabetes was determined after adjusting for demographic changes in the study population, including age, proportion enrolled in managed care, and urban residence. Results.–The adjusted prevalence of diabetes overall increased from 183 (95% confidence interval [CI], 169 –198) cases per
100 000 enrollees in 1998 to 218 (95% CI, 208 –228) cases per 100 000 enrollees in 2002, primarily because of an increase in type 1 diabetes (based on both encounter and pharmacy claims, 135 [95% CI, 123–148] cases per 100 000 enrollees in 1998 to 167 [95% CI, 158 –176] cases per 100 000 enrollees in 2002). Conclusions.–Our estimate of the overall prevalence of diabetes is consistent with national data. However, our finding that rising prevalence of type 1 diabetes appear to account for most of the increase in diabetes claims is surprising. Future research will be needed to validate these results. KEY WORDS: diabetes mellitus type 1; diabetes mellitus type 2; health expenditures; health services research; prevalence Ambulatory Pediatrics 2006;6:178 –181
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useful in tracking the prevalence and predictors of diabetes in adults,8 NHANES does not have sufficient statistical power to evaluate trends in diabetes among children. Our knowledge about the prevalence of diabetes by type is based on small population studies or clinic registries. These studies suggest an increase of type 2 diabetes, especially among minority children.4 We know of only one population-based study that found an increase in type 1 diabetes, which may have been due to an earlier measles outbreak.9 Our primary objectives were to evaluate recent trends in the prevalence of childhood diabetes overall and to understand the relative contribution of type 1 and type 2 diabetes. We used health care administrative claims for this analysis because such data have sufficient sample size and include inpatient and outpatient care and pharmacy utilization.
he prevalence of type 2 diabetes mellitus among adults has been increasing because of the national obesity epidemic.1,2 Changes in obesity rates may also be leading to increases in childhood diabetes,3 either because of insulin resistance and type 2 diabetes,4 or type 1 diabetes in certain susceptible individuals.5 Monitoring trends in an emerging epidemic is central to ensuring that appropriate resources are applied for prevention and treatment, and to evaluate the impact of any interventions. Unfortunately, there are important limitations in the data currently used to monitor childhood diabetes. The 2 main sources of data used to monitor national trends in diabetes are the National Hospital Discharge Survey (NHDS) and the National Health and Nutrition Examination Survey (NHANES). According to the NHDS, there was a 65% relative increase in the proportion of hospital discharges for diabetes between 1979 and 1999, from 1.43% to 2.36%.6 These findings, however, cannot be converted into prevalence. In contrast, NHANES is not dependent on hospitalization and includes laboratory testing, allowing identification of those with clinically recognized and unrecognized diabetes. According to NHANES, the prevalence of diabetes from 1999 –2000 among those younger than 20 was 260 per 100 000 persons.7 Although NHANES has been
METHODS Study Design We conducted a serial cross-sectional study. This study was approved by the University of Michigan Medical School institutional review board. Data Source We used the MarketScan commercial claims and encounters database (Thomson Medstat Inc, Ann Arbor, Mich), a proprietary database of person-level health care utilization and expenditure data regarding privately insured individuals from more than 60 large US employers distributed across the United States, and includes more than 200 different health plans.10 These data are primarily used by employers to assess quality and costs of health
From the Child Health Evaluation and Research Unit, Division of General Pediatrics (Drs Kemper, Dombkowski, and Davis), and Division of Pediatric Endocrinology, Diabetes, and Metabolism, University of Michigan (Dr Menon), Ann Arbor, Mich. Address correspondence to Alex R. Kemper, MD, MPH, MS, 6E18 300 North Ingalls Building, Ann Arbor, MI 48109-0456 (e-mail: [email protected]). Received for publication October 31, 2005; accepted January 15, 2006.
AMBULATORY PEDIATRICS Copyright © 2006 by Ambulatory Pediatric Association
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Table 1. Subject Characteristics by Study Year Characteristic
1998 (n ⫽ 306 991)
1999 (n ⫽ 499 334)
2000 (n ⫽ 545 451)
2001 (n ⫽ 597 686)
2002 (n ⫽ 974 407)
P Value
Age, y, mean (SD) Male sex, % Managed care, % Urban residence, %
9.8 (5.0) 51.2 70.6 73.4
10.2 (5.1) 51.1 75.6 68.2
10.2 (5.1) 51.3 79.5 71.3
10.1 (5.1) 51.3 83.4 82.4
10.2 (5.1) 51.1 87.4 81.5
.001 .05 .001 .001
plans. The MarketScan database captures all inpatient and outpatient services and pharmacy claims for a subset of individuals. For each individual, the database includes sex, date of birth, zip code, health plan characteristics, dates of enrollment, and whether claims were also coordinated with other insurance plans not included in the MarketScan database. No other demographic data, including race/ethnicity or measures of socioeconomic status, are available. The number of individuals in the database has increased over time because of the inclusion of more employers and their health plans. Study Population We included children ⱕ18 years old. We excluded children if their pharmacy claims were not available. To ensure that our study captured all relevant health care utilization events, we also excluded children who had more than a 30-day interruption in coverage or if their health care benefits were coordinated with a separate insurance plan not in the MarketScan database. Outcome Measures The main outcome measure for this study was claims evidence of any inpatient care or outpatient office visits for diabetes mellitus, based on the ICD-9-CM code for diabetes (250.XX).11 We did not consider children to have diabetes if they had a laboratory tests with an associated ICD-9-CM code for diabetes but no inpatient care or outpatient office visit claim for diabetes, because this would likely represent screening or diagnostic testing only. We used 2 different strategies to categorize children as having type 1 or type 2 diabetes. Our encounter claims only scheme was based on the fifth digit of the code for diabetes. The fifth digit of the ICD-9-CM code is specific for type 1 diabetes: 1 indicates type 1 diabetes that is not stated as uncontrolled, and 3 indicates type 1 that is uncontrolled. However, the fifth digit lacks specificity for type 2 diabetes: 0 indicates type 2 or unspecified type that is not stated as uncontrolled, and 2 indicates type 2 or unspecified type that is uncontrolled. Therefore, we classified children as having type 1 diabetes if they had any inpatient care or outpatient office visits with the codes 250.X1 or 250.X3. We classified children as having type 2 diabetes if they had any inpatient or outpatient office visits with the codes 250.X0 or 250.X2 and had no claims for 250.X1 or 250.X3. Our encounter and pharmacy claims classification scheme categorized children as having type 1 diabetes if they had any inpatient or outpatient visit for diabetes and
if they received insulin, the mainstay of treatment for type 1 diabetes. Children who had any inpatient or outpatient visit for diabetes but did not receive insulin were classified as having type 2 diabetes. Our secondary outcomes was the use of other diabetesspecific medications, including sulfonamides, and insulinsensitizing agents (eg, metformin, pioglitazone, rosiglitazone, troglitazone). These medications were not used to classify cases of diabetes. Independent Variables Independent variables included study year, age, sex, insurance type (fee for service vs managed care), and urban/rural status. Urban residence was based on whether the child lived within a metropolitan statistical area.12 We did not consider obesity in our analyses because it is not consistently identified in administrative claims.13 Statistical Analysis We evaluated changes in demographic characteristics of enrollees across the study years by the 2 tests of significance. The statistic was used to measure agreement between the 2 classification schemes for diabetes type. We calculated the prevalence of diabetes per 100 000 enrollees and 95% confidence interval on the basis of the exact binomial distribution. We then determined the prevalence adjusted for changes in demographics in the data. To do this, we first developed logistic regression models to predict the adjusted odds of diabetes, either overall or by type on the basis of the 2 classification schemes. The HuberWhite sandwich estimator was used to adjust for the clustering of individuals who appear in the data in multiple years. In these models, age was categorized as 0 – 4 years, 5–9 years, 10 –14 years, and 15–18 years. We considered P ⬍ .05 to be significant. Stata 8.2 (StataCorp, College Station, Tex) was used for all analyses. RESULTS Subject Population Subject characteristics are listed in Table 1. There was variation across the study years in age, the proportion enrolled in managed care, and the proportion with urban residence. Across all 5 study years, there were 6917 children who had at least one inpatient or outpatient claim for diabetes. Classification of Cases When we used our encounter claims only scheme for classifying type of diabetes, 5829 (84.3%) were classified
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Kemper et al
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Figure 1. Graph illustrating number of children in each study year per 100 000 enrollees with claims for diabetes overall (“overall”) and by type, as classified by encounter claims only (“encounter”) or by encounter and pharmacy claims (“insulin use” vs “no insulin use”). Error bars represent 95% confidence intervals.
with type 1 diabetes (4437 with only claims specific for type 1 diabetes ⫹ 1392 with both claims specific for type 1 diabetes and claims for type 2 diabetes/type not specified). The remaining 1088 children (15.7%) were classified with type 2 diabetes because they only had diabetes claims for type 2 diabetes/type not specified. When the encounter and pharmacy claims scheme were used, 5415 (78.3%) were classified with type 1 diabetes (ie, insulin use) and 1502 (21.7%) were classified with type 2 diabetes (ie, no insulin use). There was agreement between these classification schemes for 87.2% of subjects ( ⫽ 0.58). Differences in classifications were due to 651 subjects (9.4%) who were classified with type 1 diabetes on the basis of encounter claims only who did not receive insulin, and 237 subjects (3.4%) who were classified with type 2 diabetes on the basis of encounter claims only but who did receive insulin. Trends in Claims The Figure illustrates the unadjusted prevalence of diabetes in each study year overall and by type on the basis of the 2 classification schemes. Table 2 presents these data adjusted for age, enrollment in managed care, and urban residence. The unadjusted number of children with claims for diabetes increased from 207 cases per 100 000 enrollees in 1998 to 260 cases per 100 000 enrollees in 2002. Although the overall trend was statistically significant, the
year-to-year trend was not significant for 1998 to 1999 (P ⫽ .69), 1999 to 2000 (P ⫽ .10), or 2000 to 2001 (P ⫽ .10). In contrast, the increase from 2001 to 2002 was significant (P ⫽ .03). The adjusted prevalence was slightly lower; however, adjustment did not alter the overall trends. Most children were classified as having type 1 diabetes under both schemes in each study year. Compared to the encounter claims only classification scheme, the encounter and pharmacy claims scheme led to slightly fewer children classified as having type 1 diabetes and slightly more children having type 2 diabetes. Regardless of classification scheme or statistical adjustment, the overall increase in the number of children with claims for diabetes was primarily caused by increases in type 1 diabetes. Diabetes-Specific Pharmacy Utilization Among those with diabetes, regardless of type, 78.8% received insulin, 5.2% received an insulin-sensitizing agent, and 1.3% received a sulfonamide. However, 10.5% of those classified as type 1 diabetes on the basis of the encounter-only scheme did not receive insulin. Most of those with type 2 diabetes received no diabetes-specific medication (encounter claims only, 61.7%; encounter and pharmacy claims, 85.6%). Use of insulin-sensitizing agents or sulfonamides was rare among those with type 1 diabetes regardless of classification scheme (⬍3.5%). In contrast, approximately 12% of those classified as having type 2 diabetes by either scheme had claims for an insulinsensitizing agent and approximately 5% had claims for a sulfonamide. DISCUSSION We found the overall prevalence of diabetes to be similar to that reported from NHANES,7 and that the prevalence increased over the study period as a result of increases in type 1 diabetes. Unfortunately, few data are available to benchmark prevalence estimates by type; however, small clinic-based studies have reported the opposite: an increase in the relative proportion of type 2 compared with type 1 diabetes.14,15 There are 4 possible explanations for the greater relative increase in type 1 diabetes, which are not mutually exclusive: there may be true differences emerging in the prevalence by type of diabetes; our database of privately insured children may underestimate the contribution of type 2 diabetes because of its higher prevalence among
Table 2. Number of Children in Each Study Year per 100,000 Enrollees* Type 1
Type 2
Year
Overall
Encounter
Insulin Use
Encounter
No Insulin Use
1998 1999 2000 2001 2002
183 (169–198) 179 (168–191) 191 (180–203) 206 (194–218) 218 (208–228)
153 (140–167) 147 (137–158) 163 (153–174) 174 (163–185) 181 (172–190)
135 (123–148) 129 (120–139) 146 (136–156) 155 (145–166) 167 (158–176)
28 (23–34) 30 (26–35) 27 (23–31) 30 (26–35) 35 (32–39)
45 (39–53) 47 (42–54) 43 (38–48) 47 (42–53) 47 (43–52)
*Assessed were enrollees with claims for diabetes overall (“overall”) and by type, as classified by encounter claims only (“encounter”) or by encounter and pharmacy claims (“insulin use” vs “no insulin use”) adjusted for age, enrollment in managed care, and urban residency. The 95% confidence intervals are in parentheses.
AMBULATORY PEDIATRICS
lower income and minority children;4 there may be misclassification resulting from the clinical challenge of identifying type; and classification by administrative claims may misclassify some children. There are several limitations that could lead to misclassification: administrative claims data, even when drawn from a national sample of health plans, are not necessarily nationally representative; incomplete or inaccurate coding would bias results; ICD-9-CM does not have a code specific for type 2 diabetes;11 and clinical data are not available to validate findings. Furthermore, classification of diabetes type can be challenging in some children,16 and the prevalence of type 2 diabetes may be underestimated because early signs may be subtle. We are not able to review the study subjects’ medical records. To compensate for this, we used 2 different schemes to classify type of diabetes. We believe that the encounter claims only scheme resulted in more misclassification than the encounter and pharmacy claims scheme because approximately 10% of those classified as having type 1 diabetes according to the encounter claims only scheme did not use insulin. In contrast, the encounter and pharmacy claims scheme would misclassify children with type 2 diabetes who were treated with insulin. Both classification schemes, however, had moderate agreement and yielded similar prevalence results. Future large-scale studies are needed to better characterize the epidemiology of childhood diabetes. In addition, research is needed to identify best practices for the pharmacologic management of diabetes. We found that some children we classified as having type 2 diabetes were treated with insulin-sensitizing agents or sulfonamides; however, little is known about the potential benefits or harms of these medications when used in children.17,18 REFERENCES 1. Hedley AA, Ogden CL, Johnson CL, et al. Prevalence of overweight and obesity among US children, adolescents, and adults, 1999 –2002. JAMA. 2004;291:2847–2850.
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181
2. Mokdad AH, Ford ES, Bowman BA, et al. Prevalence of obesity, diabetes, and obesity-related health risk factors, 2001. JAMA. 2003; 289:76 –79. 3. Ludwig DS, Ebbeling CB. Type 2 diabetes mellitus in children: primary care and public health considerations. JAMA. 2001;286: 1427–1430. 4. Bloomgarden ZT. Type 2 diabetes in the young: the evolving epidemic. Diabetes Care. 2004;27:998 –1010. 5. Kibirige M, Metcalf B, Renuka R, Wilkin TJ. Testing the accelerator hypothesis. Diabetes Care. 2003;26:2865–2870. 6. Wang G, Dietz WH. Economic burden of obesity in youths aged 6 to 17 years: 1979 –1999. Pediatrics. 2002;109:e81. 7. Centers for Disease Control and Prevention. National diabetes fact sheet. Available at: http://www.cdc.gov/diabetes/pubs/estimates.htm. Accessed February 11, 2006. 8. Cowie CC, Rust KF, Byrd-Holt D, et al. Prevalence of diabetes and impaired fasting glucose in adults—United States, 1999 –2000. Morb Mortal Wkly Rep. 2003;52:833– 837. 9. Lipman TH, Chang Y, Murphy KM. The epidemiology of type 1 diabetes in children in Philadelphia, 1990 –1994. Diabetes Care. 2002;25:1969 –1975. 10. Thomson Medstat. Medstat MarketScan Databases. Available at: http://www.medstat.com/1products/marketscan.asp. Accessed February 11, 2006. 11. American Medical Association. AMA Physician ICD-9-CM 2005. Chicago, Ill: AMA Press; 2004. 12. US Census Bureau. Metropolitan and micropolitan statistical area definitions. Available at: http://www.census.gov/population/www/ estimates/metrodef.html. Accessed February 11, 2006. 13. Kaplan LM, Fallon JA, Mun EC, et al. Coding and reimbursement for weight loss surgery: best practice recommendations. Obes Res. 2005;13:290 –300. 14. Macaluso CJ, Bauer UE, Deeb LC, et al. Type 2 diabetes mellitus among Florida children and adolescents, 1994 –1998. Public Health Rep. 2002;111:373–379. 15. Pinhas-Hamiel O, Dolan LM, Daniels SR, et al. Increased incidence of non–insulin-dependent diabetes mellitus among adolescents. J Pediatr. 1996;128:608 – 615. 16. Rosenbloom AL. Obesity, insulin resistance, -cell autoimmunity, and the changing clinical epidemiology of childhood diabetes. Diabetes Care. 2003;26:2954 –2956. 17. American Diabetes Association. Type 2 diabetes in children and adolescents. Pediatrics. 2000;105:671– 680. 18. American Diabetes Association. Standards of medical care in diabetes. Diabetes Care. 2005;28:S4 –S36.
100 000 enrollees in 1998 to 218 (95% CI, 208 –228) cases per 100 000 enrollees in 2002, primarily because of an increase in type 1 diabetes (based on both encounter and pharmacy claims, 135 [95% CI, 123–148] cases per 100 000 enrollees in 1998 to 167 [95% CI, 158 –176] cases per 100 000 enrollees in 2002). Conclusions.–Our estimate of the overall prevalence of diabetes is consistent with national data. However, our finding that rising prevalence of type 1 diabetes appear to account for most of the increase in diabetes claims is surprising. Future research will be needed to validate these results. KEY WORDS: diabetes mellitus type 1; diabetes mellitus type 2; health expenditures; health services research; prevalence Ambulatory Pediatrics 2006;6:178 –181
T
useful in tracking the prevalence and predictors of diabetes in adults,8 NHANES does not have sufficient statistical power to evaluate trends in diabetes among children. Our knowledge about the prevalence of diabetes by type is based on small population studies or clinic registries. These studies suggest an increase of type 2 diabetes, especially among minority children.4 We know of only one population-based study that found an increase in type 1 diabetes, which may have been due to an earlier measles outbreak.9 Our primary objectives were to evaluate recent trends in the prevalence of childhood diabetes overall and to understand the relative contribution of type 1 and type 2 diabetes. We used health care administrative claims for this analysis because such data have sufficient sample size and include inpatient and outpatient care and pharmacy utilization.
he prevalence of type 2 diabetes mellitus among adults has been increasing because of the national obesity epidemic.1,2 Changes in obesity rates may also be leading to increases in childhood diabetes,3 either because of insulin resistance and type 2 diabetes,4 or type 1 diabetes in certain susceptible individuals.5 Monitoring trends in an emerging epidemic is central to ensuring that appropriate resources are applied for prevention and treatment, and to evaluate the impact of any interventions. Unfortunately, there are important limitations in the data currently used to monitor childhood diabetes. The 2 main sources of data used to monitor national trends in diabetes are the National Hospital Discharge Survey (NHDS) and the National Health and Nutrition Examination Survey (NHANES). According to the NHDS, there was a 65% relative increase in the proportion of hospital discharges for diabetes between 1979 and 1999, from 1.43% to 2.36%.6 These findings, however, cannot be converted into prevalence. In contrast, NHANES is not dependent on hospitalization and includes laboratory testing, allowing identification of those with clinically recognized and unrecognized diabetes. According to NHANES, the prevalence of diabetes from 1999 –2000 among those younger than 20 was 260 per 100 000 persons.7 Although NHANES has been
METHODS Study Design We conducted a serial cross-sectional study. This study was approved by the University of Michigan Medical School institutional review board. Data Source We used the MarketScan commercial claims and encounters database (Thomson Medstat Inc, Ann Arbor, Mich), a proprietary database of person-level health care utilization and expenditure data regarding privately insured individuals from more than 60 large US employers distributed across the United States, and includes more than 200 different health plans.10 These data are primarily used by employers to assess quality and costs of health
From the Child Health Evaluation and Research Unit, Division of General Pediatrics (Drs Kemper, Dombkowski, and Davis), and Division of Pediatric Endocrinology, Diabetes, and Metabolism, University of Michigan (Dr Menon), Ann Arbor, Mich. Address correspondence to Alex R. Kemper, MD, MPH, MS, 6E18 300 North Ingalls Building, Ann Arbor, MI 48109-0456 (e-mail: [email protected]). Received for publication October 31, 2005; accepted January 15, 2006.
AMBULATORY PEDIATRICS Copyright © 2006 by Ambulatory Pediatric Association
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Volume 6, Number 3 May–June 2006
AMBULATORY PEDIATRICS
Diabetes in Privately Insured Children
179
Table 1. Subject Characteristics by Study Year Characteristic
1998 (n ⫽ 306 991)
1999 (n ⫽ 499 334)
2000 (n ⫽ 545 451)
2001 (n ⫽ 597 686)
2002 (n ⫽ 974 407)
P Value
Age, y, mean (SD) Male sex, % Managed care, % Urban residence, %
9.8 (5.0) 51.2 70.6 73.4
10.2 (5.1) 51.1 75.6 68.2
10.2 (5.1) 51.3 79.5 71.3
10.1 (5.1) 51.3 83.4 82.4
10.2 (5.1) 51.1 87.4 81.5
.001 .05 .001 .001
plans. The MarketScan database captures all inpatient and outpatient services and pharmacy claims for a subset of individuals. For each individual, the database includes sex, date of birth, zip code, health plan characteristics, dates of enrollment, and whether claims were also coordinated with other insurance plans not included in the MarketScan database. No other demographic data, including race/ethnicity or measures of socioeconomic status, are available. The number of individuals in the database has increased over time because of the inclusion of more employers and their health plans. Study Population We included children ⱕ18 years old. We excluded children if their pharmacy claims were not available. To ensure that our study captured all relevant health care utilization events, we also excluded children who had more than a 30-day interruption in coverage or if their health care benefits were coordinated with a separate insurance plan not in the MarketScan database. Outcome Measures The main outcome measure for this study was claims evidence of any inpatient care or outpatient office visits for diabetes mellitus, based on the ICD-9-CM code for diabetes (250.XX).11 We did not consider children to have diabetes if they had a laboratory tests with an associated ICD-9-CM code for diabetes but no inpatient care or outpatient office visit claim for diabetes, because this would likely represent screening or diagnostic testing only. We used 2 different strategies to categorize children as having type 1 or type 2 diabetes. Our encounter claims only scheme was based on the fifth digit of the code for diabetes. The fifth digit of the ICD-9-CM code is specific for type 1 diabetes: 1 indicates type 1 diabetes that is not stated as uncontrolled, and 3 indicates type 1 that is uncontrolled. However, the fifth digit lacks specificity for type 2 diabetes: 0 indicates type 2 or unspecified type that is not stated as uncontrolled, and 2 indicates type 2 or unspecified type that is uncontrolled. Therefore, we classified children as having type 1 diabetes if they had any inpatient care or outpatient office visits with the codes 250.X1 or 250.X3. We classified children as having type 2 diabetes if they had any inpatient or outpatient office visits with the codes 250.X0 or 250.X2 and had no claims for 250.X1 or 250.X3. Our encounter and pharmacy claims classification scheme categorized children as having type 1 diabetes if they had any inpatient or outpatient visit for diabetes and
if they received insulin, the mainstay of treatment for type 1 diabetes. Children who had any inpatient or outpatient visit for diabetes but did not receive insulin were classified as having type 2 diabetes. Our secondary outcomes was the use of other diabetesspecific medications, including sulfonamides, and insulinsensitizing agents (eg, metformin, pioglitazone, rosiglitazone, troglitazone). These medications were not used to classify cases of diabetes. Independent Variables Independent variables included study year, age, sex, insurance type (fee for service vs managed care), and urban/rural status. Urban residence was based on whether the child lived within a metropolitan statistical area.12 We did not consider obesity in our analyses because it is not consistently identified in administrative claims.13 Statistical Analysis We evaluated changes in demographic characteristics of enrollees across the study years by the 2 tests of significance. The statistic was used to measure agreement between the 2 classification schemes for diabetes type. We calculated the prevalence of diabetes per 100 000 enrollees and 95% confidence interval on the basis of the exact binomial distribution. We then determined the prevalence adjusted for changes in demographics in the data. To do this, we first developed logistic regression models to predict the adjusted odds of diabetes, either overall or by type on the basis of the 2 classification schemes. The HuberWhite sandwich estimator was used to adjust for the clustering of individuals who appear in the data in multiple years. In these models, age was categorized as 0 – 4 years, 5–9 years, 10 –14 years, and 15–18 years. We considered P ⬍ .05 to be significant. Stata 8.2 (StataCorp, College Station, Tex) was used for all analyses. RESULTS Subject Population Subject characteristics are listed in Table 1. There was variation across the study years in age, the proportion enrolled in managed care, and the proportion with urban residence. Across all 5 study years, there were 6917 children who had at least one inpatient or outpatient claim for diabetes. Classification of Cases When we used our encounter claims only scheme for classifying type of diabetes, 5829 (84.3%) were classified
180
Kemper et al
AMBULATORY PEDIATRICS
Figure 1. Graph illustrating number of children in each study year per 100 000 enrollees with claims for diabetes overall (“overall”) and by type, as classified by encounter claims only (“encounter”) or by encounter and pharmacy claims (“insulin use” vs “no insulin use”). Error bars represent 95% confidence intervals.
with type 1 diabetes (4437 with only claims specific for type 1 diabetes ⫹ 1392 with both claims specific for type 1 diabetes and claims for type 2 diabetes/type not specified). The remaining 1088 children (15.7%) were classified with type 2 diabetes because they only had diabetes claims for type 2 diabetes/type not specified. When the encounter and pharmacy claims scheme were used, 5415 (78.3%) were classified with type 1 diabetes (ie, insulin use) and 1502 (21.7%) were classified with type 2 diabetes (ie, no insulin use). There was agreement between these classification schemes for 87.2% of subjects ( ⫽ 0.58). Differences in classifications were due to 651 subjects (9.4%) who were classified with type 1 diabetes on the basis of encounter claims only who did not receive insulin, and 237 subjects (3.4%) who were classified with type 2 diabetes on the basis of encounter claims only but who did receive insulin. Trends in Claims The Figure illustrates the unadjusted prevalence of diabetes in each study year overall and by type on the basis of the 2 classification schemes. Table 2 presents these data adjusted for age, enrollment in managed care, and urban residence. The unadjusted number of children with claims for diabetes increased from 207 cases per 100 000 enrollees in 1998 to 260 cases per 100 000 enrollees in 2002. Although the overall trend was statistically significant, the
year-to-year trend was not significant for 1998 to 1999 (P ⫽ .69), 1999 to 2000 (P ⫽ .10), or 2000 to 2001 (P ⫽ .10). In contrast, the increase from 2001 to 2002 was significant (P ⫽ .03). The adjusted prevalence was slightly lower; however, adjustment did not alter the overall trends. Most children were classified as having type 1 diabetes under both schemes in each study year. Compared to the encounter claims only classification scheme, the encounter and pharmacy claims scheme led to slightly fewer children classified as having type 1 diabetes and slightly more children having type 2 diabetes. Regardless of classification scheme or statistical adjustment, the overall increase in the number of children with claims for diabetes was primarily caused by increases in type 1 diabetes. Diabetes-Specific Pharmacy Utilization Among those with diabetes, regardless of type, 78.8% received insulin, 5.2% received an insulin-sensitizing agent, and 1.3% received a sulfonamide. However, 10.5% of those classified as type 1 diabetes on the basis of the encounter-only scheme did not receive insulin. Most of those with type 2 diabetes received no diabetes-specific medication (encounter claims only, 61.7%; encounter and pharmacy claims, 85.6%). Use of insulin-sensitizing agents or sulfonamides was rare among those with type 1 diabetes regardless of classification scheme (⬍3.5%). In contrast, approximately 12% of those classified as having type 2 diabetes by either scheme had claims for an insulinsensitizing agent and approximately 5% had claims for a sulfonamide. DISCUSSION We found the overall prevalence of diabetes to be similar to that reported from NHANES,7 and that the prevalence increased over the study period as a result of increases in type 1 diabetes. Unfortunately, few data are available to benchmark prevalence estimates by type; however, small clinic-based studies have reported the opposite: an increase in the relative proportion of type 2 compared with type 1 diabetes.14,15 There are 4 possible explanations for the greater relative increase in type 1 diabetes, which are not mutually exclusive: there may be true differences emerging in the prevalence by type of diabetes; our database of privately insured children may underestimate the contribution of type 2 diabetes because of its higher prevalence among
Table 2. Number of Children in Each Study Year per 100,000 Enrollees* Type 1
Type 2
Year
Overall
Encounter
Insulin Use
Encounter
No Insulin Use
1998 1999 2000 2001 2002
183 (169–198) 179 (168–191) 191 (180–203) 206 (194–218) 218 (208–228)
153 (140–167) 147 (137–158) 163 (153–174) 174 (163–185) 181 (172–190)
135 (123–148) 129 (120–139) 146 (136–156) 155 (145–166) 167 (158–176)
28 (23–34) 30 (26–35) 27 (23–31) 30 (26–35) 35 (32–39)
45 (39–53) 47 (42–54) 43 (38–48) 47 (42–53) 47 (43–52)
*Assessed were enrollees with claims for diabetes overall (“overall”) and by type, as classified by encounter claims only (“encounter”) or by encounter and pharmacy claims (“insulin use” vs “no insulin use”) adjusted for age, enrollment in managed care, and urban residency. The 95% confidence intervals are in parentheses.
AMBULATORY PEDIATRICS
lower income and minority children;4 there may be misclassification resulting from the clinical challenge of identifying type; and classification by administrative claims may misclassify some children. There are several limitations that could lead to misclassification: administrative claims data, even when drawn from a national sample of health plans, are not necessarily nationally representative; incomplete or inaccurate coding would bias results; ICD-9-CM does not have a code specific for type 2 diabetes;11 and clinical data are not available to validate findings. Furthermore, classification of diabetes type can be challenging in some children,16 and the prevalence of type 2 diabetes may be underestimated because early signs may be subtle. We are not able to review the study subjects’ medical records. To compensate for this, we used 2 different schemes to classify type of diabetes. We believe that the encounter claims only scheme resulted in more misclassification than the encounter and pharmacy claims scheme because approximately 10% of those classified as having type 1 diabetes according to the encounter claims only scheme did not use insulin. In contrast, the encounter and pharmacy claims scheme would misclassify children with type 2 diabetes who were treated with insulin. Both classification schemes, however, had moderate agreement and yielded similar prevalence results. Future large-scale studies are needed to better characterize the epidemiology of childhood diabetes. In addition, research is needed to identify best practices for the pharmacologic management of diabetes. We found that some children we classified as having type 2 diabetes were treated with insulin-sensitizing agents or sulfonamides; however, little is known about the potential benefits or harms of these medications when used in children.17,18 REFERENCES 1. Hedley AA, Ogden CL, Johnson CL, et al. Prevalence of overweight and obesity among US children, adolescents, and adults, 1999 –2002. JAMA. 2004;291:2847–2850.
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2. Mokdad AH, Ford ES, Bowman BA, et al. Prevalence of obesity, diabetes, and obesity-related health risk factors, 2001. JAMA. 2003; 289:76 –79. 3. Ludwig DS, Ebbeling CB. Type 2 diabetes mellitus in children: primary care and public health considerations. JAMA. 2001;286: 1427–1430. 4. Bloomgarden ZT. Type 2 diabetes in the young: the evolving epidemic. Diabetes Care. 2004;27:998 –1010. 5. Kibirige M, Metcalf B, Renuka R, Wilkin TJ. Testing the accelerator hypothesis. Diabetes Care. 2003;26:2865–2870. 6. Wang G, Dietz WH. Economic burden of obesity in youths aged 6 to 17 years: 1979 –1999. Pediatrics. 2002;109:e81. 7. Centers for Disease Control and Prevention. National diabetes fact sheet. Available at: http://www.cdc.gov/diabetes/pubs/estimates.htm. Accessed February 11, 2006. 8. Cowie CC, Rust KF, Byrd-Holt D, et al. Prevalence of diabetes and impaired fasting glucose in adults—United States, 1999 –2000. Morb Mortal Wkly Rep. 2003;52:833– 837. 9. Lipman TH, Chang Y, Murphy KM. The epidemiology of type 1 diabetes in children in Philadelphia, 1990 –1994. Diabetes Care. 2002;25:1969 –1975. 10. Thomson Medstat. Medstat MarketScan Databases. Available at: http://www.medstat.com/1products/marketscan.asp. Accessed February 11, 2006. 11. American Medical Association. AMA Physician ICD-9-CM 2005. Chicago, Ill: AMA Press; 2004. 12. US Census Bureau. Metropolitan and micropolitan statistical area definitions. Available at: http://www.census.gov/population/www/ estimates/metrodef.html. Accessed February 11, 2006. 13. Kaplan LM, Fallon JA, Mun EC, et al. Coding and reimbursement for weight loss surgery: best practice recommendations. Obes Res. 2005;13:290 –300. 14. Macaluso CJ, Bauer UE, Deeb LC, et al. Type 2 diabetes mellitus among Florida children and adolescents, 1994 –1998. Public Health Rep. 2002;111:373–379. 15. Pinhas-Hamiel O, Dolan LM, Daniels SR, et al. Increased incidence of non–insulin-dependent diabetes mellitus among adolescents. J Pediatr. 1996;128:608 – 615. 16. Rosenbloom AL. Obesity, insulin resistance, -cell autoimmunity, and the changing clinical epidemiology of childhood diabetes. Diabetes Care. 2003;26:2954 –2956. 17. American Diabetes Association. Type 2 diabetes in children and adolescents. Pediatrics. 2000;105:671– 680. 18. American Diabetes Association. Standards of medical care in diabetes. Diabetes Care. 2005;28:S4 –S36.