December 3, 2008
People with blood glucose levels that are higher than normal but not yet in the diabetic range have "prediabetes." Doctors sometimes call this condition impaired fasting glucose (IFG) or impaired glucose tolerance (IGT), depending on the test used to diagnose it. Insulin resistance and prediabetes usually have no symptoms. You may have one or both conditions for several years without noticing anything.
At present, the fasting plasma glucose (FPG) and the 2-h oral glucose tolerance test (OGTT) are the tests of choice to identify all states of hyperglycemia. Either test is suitable, and each has advantages and disadvantages, such as convenience, cost, and reproducibility. Identification of individuals with IGT can be made only with a 2-hour OGTT; the fasting plasma glucose (FPG) alone will miss approximately 30% of patients with isolated IGT. A recent consensus statement issued by the American Diabetes Association has recommended that if pharmacotherapy is used, both IFG and IGT should be documented. If only lifestyle modification is planned, a confirmatory test is not required.5,4
See Table 1 for the tests and corresponding glucose values used to identify IGT and IFG.
Table 1 -- Identifying Prediabetes: IGT and IFG7
|Condition/Classification||Test Used and Diagnostic Values|
|Impaired Glucose Tolerance (IGT)||
|Impaired Fasting Glucose (IFG)||
About 54 million individuals in the United States aged 21 years and older have prediabetes,3 nearly 12 million of whom are overweight and between the ages of 45-74.6 In addition to the nearly 21 million individuals in the United States currently diagnosed with diabetes, the estimated number of diagnosed cases of diabetes will increase in the United States by 198% in the next 50 years?with the largest increase occurring among African Americans, American Indians, and Hispanic/Latino Americans.8
Screening for prediabetes (IFG/IGT) is fundamentally no different from screening for diabetes because the same risk factors are associated with both conditions.5,9 See Table 2 for specific recommendations for prediabetes screening, as well as relevant prediabetes/type 2 diabetes risk factors.
Table 2 -- Prediabetes Screening Guidelines
|Recommending Body||Prediabetes risk factors and screening guidelines|
American Diabetes Association (ADA)
Recommended tests: FPG or 2-h OGTT
1. All persons ≥45 years of age, particularly in those who are overweight (BMI>25kg/m2), and repeated every three years
2. Persons <45 years of age who are overweight (BMI>25kg/m2) with any one of the following risk factors:9
Indian Health Services (IHS)
Recommended tests: FPG in the morning or 2-hr OGTT
1. Annual testing of American Indian and Alaska Native adults aged 19 years and older with any of the following risk factors for diabetes:7
2. Testing every three years beginning at age 35 for those without the above risk-factors
The U.S Preventive Services Task Force also makes recommendations related to screening for diabetes and that recommendation can be found at: www.ahrq.gov/clinic/uspstf/uspsdiab.htm.
No, risk factors for prediabetes do not differ from type 2 diabetes. Both conditions share the same risk factors, and prediabetes is itself a risk factor for type 2 diabetes.5,9 See Table 2 for prediabetes/type 2 diabetes risk factors.
While prediabetes and type 2 diabetes share the same risk factors, persons with prediabetes can reduce their blood glucose levels to normal values and reduce their risk for developing type 2 diabetes. Currently, there is not enough information to warrant distinguishing prediabetes and diabetes' risk factors. As we learn more about the differing pathophysiologies of IGT and IFG and their relation to the onset of type 2 diabetes, as well as preventive interventions, distinguishing prediabetes and type 2 diabetes risk factors might become possible.
The risk of progressing to diabetes depends on the type of prediabetes that a person has (IFG only, IGT only, or both), as well as other diabetes risk factors. Individuals with prediabetes who are older, overweight, and have a family history of diabetes and gestational diabetes are more likely to progre-ss to diabetes.5 Individuals with prediabetes are 5-15 times more likely to develop type 2 diabetes than are people with normal glucose values.4 Individuals with both IFG and IGT develop diabetes approximately twice as often as individuals with just one of the two conditions.5
Annual progression to diabetes
Studies in the United States and abroad show that, for persons with IGT, between 2% and 34% will develop type 2 diabetes annually; for persons with IFG, between 1.5% and 23% will develop diabetes annually.4 Two randomized controlled trials of diabetes prevention, the Diabetes Prevention Program (DPP) and the Finish Diabetes Prevention Study, demonstrated that 3-5% of individuals with IGT who lost weight and engaged in moderate physical activity progressed to diabetes annually. For persons with prediabetes who did not lose weight and engage in moderate physical activity, 11% progressed to diabetes annually.10-11
Prolonged progression to diabetes
The natural history of prediabetes (both IGT and IFG) indicates that about 25% of persons with prediabetes progress to diabetes within three to five years. With longer observation, the majority of individuals with IFG or IGT go on to develop diabetes5 within about 10 years, unless they lose weight through moderate changes in diet and physical activity.12 Over the course of a lifetime, as many as 83% of persons with prediabetes (IGT) who neither lose weight nor engage in moderate physical activity will develop diabetes.13 Over the course of a lifetime, approximately 65% of persons with prediabetes who lose weight and engage in moderate physical activity will go on to develop diabetes13-14
Progression to diabetes among the general population in the United States
The annual risk of developing diabetes for the average person living in the United States with normal glucose levels is about 0.7% per year.15 For individuals born in the United States in 2000, the estimated lifetime risk of being diagnosed with diabetes is roughly 1 of 3 for males and 2 of 5 for females. The lifetime risk of diabetes is even greater for ethnic minorities: 2 of 5 African Americans and Hispanics, and 1 of 2 Hispanic females, will develop the disease.3 With lifestyle changes, this course can be changed.
Interventions to prevent or delay prediabetes from progressing to type 2 diabetes can be feasible and cost-effective, and many individuals in the United States could benefit from them, particularly those who are overweight or obese.16
Developing type 2 diabetes is not inevitable. A variety of clinical trials demonstrate that individuals with prediabetes can prevent or delay the progression to diabetes through lifestyle and some pharmaceutical interventions. These studies demonstrate that persons at risk for diabetes can be identified early in the disease progression, before exhibiting blood glucose values indicative of diabetes. Those individuals who lose weight and increase their physical activity can prevent or delay the development of diabetes. Moderate-intensity lifestyle interventions can delay development of type 2 diabetes by an average of 11 years and reduce the number of new cases of type 2 diabetes by 20%. Pharmacological interventions has shown to delay the onset of type 2 diabetes by an average of three years while reducing the number of new cases of type 2 diabetes by 8%.13
Lifestyle Intervention Strategies
Lifestyle changes can prevent or delay the onset of type 2 diabetes among high-risk adults. This has been shown in studies that included people with IGT and other high-risk characteristics for developing diabetes. Lifestyle interventions included low fat diet and moderate-intensity physical activity (such as walking for 2 1/2 hours each week). In the DPP, a large prevention study of people at high risk for diabetes, the development of diabetes was reduced by 58% over 3 years.17
See Table 3 for key aspects of the DPP lifestyle protocol. A comprehensive description of the DPP, including the lifestyle protocols, lifestyle manuals and an updated list of DPP-related publications can be found at www.bsc.gwu.edu/dpp/index.htmlvdoc.
Other studies have shown lifestyle education (dietary + exercise or dietary alone) can reduce 2-hour plasma glucose levels as well as the onset of type 2 diabetes among those at risk by as much as 50%.18 A listing of these lifestyle interventions can be found in Table 4.
Table 3 -- DPP Lifestyle Protocols19
|Clearly defined weight loss and physical activity goals||A flexible maintenance program|
|Individual case managers or "lifestyle coaches"||Culturally-appropriate materials and strategies|
|Intensive, ongoing intervention||Local and national network of training, feedback and clinical support|
|A core curriculum||Supervised exercise sessions at least twice weekly|
Table 4 -- Lifestyle education interventions for type 2 diabetes prevention18
|Type of Intervention||Dietary Education||Exercise Education|
|Dietary + exercise||Reducing energy intake||Increase leisure physical exercise by one of more of the following examples: 30 extra minutes per day of slow walking; 20 extra minutes per day of brisk walking; 10 extra minutes per day of jogging; 5 extra minutes per day of jumping rope, playing basketball or swimming.|
|Dietary + exercise||Standard diet advice sheet with telephone contact (three per month)||Emphasizing need for regular exercise|
|Dietary + exercise||Low-fat, high-fiber diet||Regular exercise with a program implemented during a 1-month stay at a wellness center that included intense dietary learning sessions|
|Dietary + exercise||Regular diet counseling from a dietician||Physical activity counseling from a physiotherapist|
|Dietary + exercise||Individualized dietary counseling from a nutritionist||Circuit-type resistance training sessions and advice on increasing overall physical activity|
|Dietary + exercise||Regular dietary advice||Stimulated to lose weight and increase physical activity with visits scheduled at regular intervals|
|Dietary + exercise||Weight-reduction through a healthy low-calorie, low-fat diet||Engage in physical activity of moderate intensity by individualized curriculum by case managers|
|Dietary alone||Reduced-fat diet and participation in monthly small-group education session for one year|
|Dietary alone||Reducing energy intake, especially at dinner|
The drug metformin is effective in delaying or preventing conversion of prediabetes to diabetes. However, it is not as effective as the lifestyle intervention. While the lifestyle intervention reduced diabetes onset by 58%, metformin reduced onset by 31%.10
Several clinical trials have shown reductions in the incidence of diabetes with different pharmacotherapies, though their longer-term effectiveness remains unknown. For example, rosiglitazone is a newer drug that has been shown to reduce the incidence of diabetes in 60% of individuals with elevated blood glucose levels over the reduction observed in a placebo group.20 While this drug could be effective, the main clinical trial did not compare this treatment to lifestyle change or other drugs. Rosiglitazone can have side effects; these include headaches, back pain, fatigue, hypoglycemia, hyperglycemia, and upper respiratory tract infections. A major side effect of rosiglitazone was an increased incidence of cardiovascular events, including a 7-fold increase in heart failure over what was observed in those receiving a placebo.20 Also, acarbose (another drug) was shown to delay progression to type 2 diabetes in patients with IGT by 25% over 3.3 years.21 Researchers also observed a greater than 50% reduction in the incidence of type 2 diabetes in Hispanic women who were treated with troglitazone, an insulin-sensitizing drug. These women continued to experience the protective benefits from diabetes eight months after the drug was stopped.22 Troglitazone was removed from the market due to safety concerns. As questions remain regarding the long-term efficacy and cost-effectiveness of pharmaceutical interventions for prediabetes, experts continue to recommend diet and exercise as the most effective preventive approach for people with prediabetes.5,9,20,23
Interventions to prevent or delay prediabetes from progressing to type 2 diabetes can be feasible and cost-effective. Many individuals in the United States, particularly those who are overweight or obese,16 could benefit from such interventions. As shown in Table 5, research from the DPP found that lifestyle interventions are more cost-effective than pharmacological agents.13,24
DPP Findings on Cost-Effectiveness of Interventions
|Lifestyle Intervention Strategies||Pharmacological Agent (metformin)|
a A QALY measures the cost to extend life by one healthy year. It measures not only years of life gained but also the quality of those life years.
b The health system perspective includes the cost of treatment (e.g., clinician time and medication cost).
c The societal perspective includes costs to society (e.g., indirect costs such as lost productivity and taxes paid for health care and disability, direct non-medical costs related to lifestyle changes).
The American Diabetes Association supports lifestyle modification as the best method of treating prediabetes because there is insufficient evidence to support the cost-effectiveness of medication interventions.9 The completed prevention trials indicate that an intensive lifestyle intervention provides the greatest reduction in the occurrence of diabetes, along with a modest reduction in cardiovascular disease risk factors.5
Assessing costs and savings can be a challenge in determining the best strategies for preventing diabetes among those with prediabetes. For example, lifestyle changes are usually paired with medical treatment, making it difficult to decipher which prevention strategy is most cost effective.25 Also, the brief duration of some trials limits the ability to determine long-term effects, such as morbidity (complications) or mortality.25-26
Insurance plans differ in reimbursement for diabetes and prediabetes screening and treatment. Most insurance plans cover testing for people suspected of having diabetes. Becausethe tests and risk factors are the same for both conditions, a prediabetes test may be covered.
As of 2005, the Centers for Medicare and Medicaid Services (CMS) cover screening tests for diabetes for those who have been diagnosed with prediabetes. The CMS policy covers the following:
Covered tests include the fasting blood glucose (FBG) test and the post-glucose challenge test (OGTT). Medicare-covered diabetes screening tests do not require co-payments, deductibles, or coinsurance from the Medicare member.27
Individuals who have any one of the following risk factors for diabetes are eligible for the CMS benefit:
Individuals who have at least two of the following characteristics:
Medicaid, the combined federal and state health insurance program for the poor and disabled, has no national-level requirements around screening or treatment for diabetes or prediabetes, though all states and Medicaid plans must cover physician, hospital, and lab services. Generally, the Medicaid program covers most diabetes medications but may not always cover diabetes education services, insulin pumps or prediabetes screening.28 Medicaid coverage rules are set at the state level and vary from state to state.
Private insurance generally consists of group (i.e., self-insured, employer-sponsored health insurance) and individual coverage. Individual coverage is subject to state insurance laws and mandates. As of December 2005, 46 states had laws requiring coverage of diabetes treatment in private insurance plans.29 Employer-sponsored health plans that are self-insured are exempt from these mandates through the Employee Retirement Income Security Act of 1974 (ERISA), so coverage of diabetes services varies greatly.