© 2002 by the American Diabetes Association, Inc.
Projected Impact of Implementing the Results of the Diabetes Prevention Program in the U.S. Population
1 Social and Scientific Systems, Silver Spring, Maryland
OBJECTIVETo determine the feasibility of using either fasting plasma glucose or HbA1c to identify individuals in the U.S. population who meet the Diabetes Prevention Program (DPP) criteria for intervention, defined as BMI 24 kg/m2, fasting plasma glucose level 96125 mg/dl, and 2-h glucose level 140199 mg/dl in an oral glucose tolerance test (OGTT). RESEARCH DESIGN AND METHODSAnalysis of a representative sample of U.S. adults aged 4074 years with no medical history of diabetes for whom data on height, weight, fasting plasma glucose, HbA1c, and 2-h plasma glucose during an OGTT were obtained. Sensitivity, specificity, positive predictive value (PPV), and receiver operator characteristic (ROC) curves for fasting glucose and HbA1c were determined.
RESULTSUsing BMI <24 kg/m2 as an initial criterion eliminated 27.2% of U.S. adults from further testing. Of the remaining group, 41.1% did not have to be considered for an OGTT because their fasting glucose level was below or above 96125 mg/dl. Overall, 10.6% of adults aged 4074 years without medical history of diabetes met the DPP eligibility criteria for intervention. Among individuals with BMI CONCLUSIONSUsing data on BMI and setting cutoff values for fasting glucose and HbA1c would greatly reduce the number of individuals who would need to undergo an OGTT while achieving adequate sensitivity, specificity, and PPV.
Abbreviations: DPP, Diabetes Prevention Program NHANES III, third National Health and Nutrition Examination Survey OGTT, oral glucose tolerance test PPV, positive predictive value ROC, receiver operator characteristic
The U.S. Diabetes Prevention Program (DPP) and the Diabetes Prevention Study in Finland were the first major randomized, controlled clinical trials to investigate whether type 2 diabetes could be prevented; both studies were completed in 2001. Before these studies, it was unknown whether type 2 diabetes could be prevented by lifestyle or pharmaceutical intervention. The studies indicate that metformin or lifestyle interventions can have dramatic effects in preventing type 2 diabetes. In both trials, individuals at high risk for diabetes based on BMI, fasting plasma glucose, and response to an oral glucose tolerance test (OGTT) reduced their risk of diabetes by 58% by participating in a structured physical activity and weight loss program (1,2). The risk was reduced by 31% in participants taking metformin in the DPP. The DPP intervention was applied to individuals at high risk for diabetes based on BMI 24 kg/m2, fasting plasma glucose level 96125 mg/dl, and 2-h plasma glucose level 140199 mg/dl at 2 h after an oral glucose challenge (3). It was estimated that 10 million people in the U.S. would meet these criteria and that a substantial reduction in diabetes incidence would occur if the DPP interventions were implemented in these people (1). Diabetes presents a significant public health burden associated with increased morbidity, mortality, and economic costs. Diabetes leads to increased rates of microvascular disease (retinopathy, neuropathy, renal disease, and lower extremity amputations), coronary heart disease and peripheral vascular disease, stroke, and disability and a reduced life expectancy of 78 years (4). It is estimated that $44 billion in direct costs, including inpatient care and nursing homes, was spent on diabetes in 1997 and $54 million was incurred in indirect costs, including disability and premature mortality (5). Furthermore, the prevalence of diabetes in the U.S. has increased fivefold in the past 30 years, and it is projected that 21.4 million people will have diabetes in the U.S. by 2025 (6). Because of the success of the DPP interventions and the significant public health burden presented by diabetes, a program to identify individuals at high risk for diabetes and meeting the DPP criteria would offer a method to implement a program to markedly reduce diabetes in the U.S. One barrier to identifying these individuals is the need to administer an OGTT. Currently, few physicians and patients are willing to undergo an OGTT due to the time, inconvenience, and expense of the test. Indeed, the American Diabetes Association (ADA) recommended abandonment of the OGTT as a screening and diagnostic test for diabetes (7). An alternative is to use fasting glucose or HbA1c levels to identify individuals who meet the DPP criteria. To investigate this issue, we analyzed data from a representative sample of U.S. adults to determine the sensitivity, specificity, and positive predictive value (PPV) of using fasting glucose or HbA1c or a combination of both to identify individuals who meet the DPP criteria for intervention.
Design, setting, and participants The third National Health and Nutrition Examination Survey (NHANES III) was conducted from 1988 to 1994 and included a stratified probability sample of the U.S. population (8). Participants were interviewed in their homes and underwent a standardized set of physical examinations and laboratory measurements in an examination center. After an overnight fast of 9 h, a venous blood sample was obtained and a 2-h 75-g OGTT was administered to the subset of subjects who were aged 4074 years and did not report a prior diagnosis of diabetes (n = 2,844) (9). The OGTT was only administered to NHANES III participants aged 4074 years, whereas the eligibility for DPP was 25 years of age. Consequently, we do not have information for the U.S. population aged 2539 years or for those aged 75 years.
Statistical analysis
The DPP determined eligibility for the study by administering an OGTT only to individuals with BMI 24 kg/m2 and fasting plasma glucose level 96125 mg/dl; those with 2-h glucose level 140199 mg/dl were eligible for the study (3,10). Based on NHANES III, 27.2% of the U.S. population aged 4074 years with no medical history of diabetes had BMI <24 kg/m2 and 72.8% had BMI 24 kg/m2 (Fig. 1). Of those with BMI 24 kg/m2, 6.2% had a fasting plasma glucose level 126 mg/dl and would be classified as having newly diagnosed diabetes. These individuals would be recommended for confirmatory testing for diabetes in accordance with ADA recommendations (7). Of those with BMI 24 kg/m2, 34.9% had fasting plasma glucose level <96 mg/dl and would not meet the DPP eligibility criteria for intervention and are considered to be at low risk for diabetes. The remainder (58.9%) of those with BMI 24 kg/m2 had fasting plasma glucose level 96125 mg/dl. Among those with BMI 24 kg/ m2 and fasting glucose level 96125 mg/dl, 69.6% had 2-h plasma glucose level <140 mg/dl (normal glucose tolerance), 24.8% had 2-h glucose level 140199 mg/dl (impaired glucose tolerance), and 5.6% had 2-h glucose level 200 mg/dl (newly diagnosed diabetes). Those with newly diagnosed diabetes, classified by 2-h glucose level 200 mg/dl, were recommended for further testing and treatment. In summary, among those aged 4074 years with no medical history of diabetes in the U.S. population, 10.6% would meet the DPP eligibility criteria for intervention (100% x 0.728 x 0.589 x 0.248).
Based on the ROC curve for subjects with BMI 24 kg/m2 and fasting plasma glucose level 96125 mg/dl, the area under the curve, to predict 2-h glucose level 140199 mg/dl, for fasting plasma glucose level and HbA1c was 0.665 (95% CI 0.6300.700) and 0.593 (0.5570.629), respectively, and differed significantly (P = 0.002) (Fig. 2). We stratified further to determine whether including other factors known to be associated with elevated 2-h glucose level improved the accuracy of fasting plasma glucose or HbA1c. The ROC curves after stratification by age (4059 vs. 6074 years), race (non-Hispanic white versus all others) and family history (having a first-degree relative with diabetes versus no first-degree relative) did not differ significantly. Stratifying by age, the area under the curve for fasting glucose for those aged 4059 years was 0.569 (0.5170.620) and for those aged 6074 years was 0.596 (0.5460.647; P = 0.452). Stratifying by race, the area under the curve for fasting glucose for non-Hispanic whites was 0.633 (0.5840.682) and for all others was 0.655 (0.6110.697; P = 0.522). Stratifying by family history, the area under the curve for fasting glucose for those with no family history was 0.627 (0.5870.667) and for those with a family history was 0.689 (0.6340.742; P = 0.075).
Among those with BMI 24 kg/m2 and fasting plasma glucose level 96125 mg/dl (i.e., those eligible for the OGTT in DPP), as fasting glucose values increased, the sensitivity of fasting glucose to identify individuals with 2-h glucose level 140199 mg/dl decreased, the specificity increased, and the PPV increased (Table 1). The likelihood ratio for the odds that a given cut point of fasting glucose would be expected in an individual with 2-h glucose level 140199 mg/dl was highest at fasting glucose level 115 mg/dl. At fasting glucose level 105 mg/dl, which included 37.5% of participants, the sensitivity of fasting glucose to identify the individuals with 2-h glucose of 140199 mg/dl was 56.0%, the specificity was 72.0%, and the PPV was 17.1%. Similarly, at HbA1c 5.5%, which included 38.3% of participants, the sensitivity of HbA1c to identify the individuals with 2-h glucose level 140199 mg/dl was 60.0%, the specificity was 55.0%, and the PPV was 21.4% (Table 1). Requiring both fasting glucose level 105 mg/dl and HbA1c 5.5% decreased the sensitivity to 33.4% but increased the specificity to 84.8% and PPV to 37.9%. Requiring either fasting glucose level 105 mg/dl or HbA1c 5.5% increased the sensitivity to 82.6% but decreased the specificity to 42.3% and did not substantially change the PPV (31.3%). Using a higher fasting glucose cut point of 110 mg/ dl decreased the sensitivity further, increased the specificity, and did not substantially change the PPV. Similarly, using a higher HbA1c cut point of 6.0% also decreased the sensitivity, increased the specificity, and did not substantially change the PPV (Table 2).
Increasing BMI from 24 to 27 or 30 kg/m2 resulted in an increase in sensitivity and PPV for both fasting glucose and HbA1c (Table 3). For those aged 6074 years, sensitivity, specificity, and PPV for fasting glucose and HbA1c were somewhat better than for those aged 4059 years, but the differences were not substantial. The effect of race was minor for fasting plasma glucose but, for HbA1c, non-Hispanic whites had lower sensitivity and higher specificity than all others.
Identification of individuals who would meet the criteria for a DPP intervention is both a public health and a clinical issue. It could also be an enormous undertaking, given the fact that there are 95 million people aged 4074 years without a medical history of diagnosed diabetes in the U.S. (11,12). The DPP recruited participants at high risk for developing diabetes based on BMI, fasting plasma glucose level, and response to an OGTT. To determine those who might be eligible for a DPP intervention in the general U.S. population to reduce their risk of developing diabetes, measurement of height and weight could immediately eliminate from further testing the 27.2% of individuals with BMI <24 kg/m2. Measurement of fasting plasma glucose in those with BMI 24 kg/m2 would eliminate 41.1% of this group who are below or above the DPP fasting plasma glucose criteria. For the remaining 41 million individuals with BMI 24 kg/m2 and fasting plasma glucose level 96125 mg/dl, setting the fasting glucose cutoff value at 105 mg/dl would eliminate 62.5% from further testing by the OGTT while including fully 56.0% of those with 2-h glucose level 140199 mg/dl. Thus, for the 95 million people aged 4074 years without diagnosed diabetes, 15 million would have to undergo an OGTT by this scheme. A similar procedure could be followed using HbA1c 5.5%, which does not require an individual to be fasting and can be measured in a blood sample collected without regard to time of the prior meal. If HbA1c is used, the method for measuring HbA1c would have to be standardized to the Diabetes Control and Complications (DCCT) method (13) to use the same cutoff values as in Table 1.
Although the results are representative of the U.S. population, we only have data on individuals aged 4074 years. Therefore, we cannot draw specific conclusions for those aged >74 years or <40 years. In addition, the data in NHANES III were collected from 1988 to 1994. The prevalence of being overweight or obese (BMI
Ideally, a screening test should have high sensitivity and high specificity; it is desirable to miss very few people who have the disease and to not misclassify a large number of people who do not have the disease. In the identification of people meeting the DPP criteria, these requirements may not be necessary. By using a fasting plasma glucose cutoff value of Even though individuals with BMI <24 kg/m2 would not meet the DPP criteria for intervention, there are still a number of people in this group who have elevated 2-h glucose levels and who presumably would be at increased risk for diabetes. However, because such individuals were not included in DPP, we have no information regarding whether the intervention would be effective. Furthermore, in these individuals, BMI is considered normal and a structured weight loss program may not be advisable. Few studies have examined the ability to identify individuals with abnormal glucose tolerance without administering an OGTT. Overall, these studies found that the sensitivity of fasting glucose to identify individuals with impaired glucose tolerance was fairly low (15,16) and that HbA1c was fairly specific but not very sensitive (1719). However, only one of these studies focused specifically on screening for impaired glucose tolerance (15) and none were representative of the general U.S. population. For a screening program to be effective, it must have a number of attributes: 1) the disease should represent a sizable burden to the population; 2) it should have a preclinical phase during which it can be diagnosed; and 3) it should have improved prognosis after diagnosis. Based on the promising results from DPP and the Finnish Diabetes Prevention Study, diabetes now meets all three of these attributes. Data from NHANES III provide physicians and public health officials a clearer idea of the number of OGTTs and the scope of the screening that would need to be undertaken to implement DPP. It was estimated that 10 million people in the U.S. meet the DPP criteria for eligibility for intervention and that 11.0% of these will develop diabetes in 1 year (1). Reducing the risk of diabetes by 58% within this group would significantly reduce the burden of diabetes in the U.S. and potentially prevent many complications and premature deaths.
Address correspondence and reprint requests to Sharon H. Saydah, 8757 Georgia Ave., 12th Floor, Silver Spring, MD 20910. E-mail: ssaydah{at}s-3.com. Received for publication 6 February 2002 and accepted in revised form 21 June 2002. The opinions expressed in this paper are those of the authors and do not necessarily represent the position of the National Institute of Diabetes and Digestive and Kidney Diseases. A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances. See accompanying editorial on p. 2098.
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