Vol. 15 •Issue 11
• Page 43
Altering the Course
Screening for Prediabetes
By Carey Marie Boehm, NP, and Sheila Smith, NP
Diabetes has become one of the most expensive and taxing chronic diseases in the United States. Elevated blood glucose levels increase cardiovascular disease, peripheral vascular disease, stroke and damage to eyes, kidneys and nerves.1 By the time many patients are diagnosed with type 2 diabetes, underlying vascular disease is well under way.
The treatment of diabetes has become more sophisticated and effective, but given the increasing prevalence of diabetes and its serious long-term consequences, it is important to focus on prevention.
Prediabetes is defined as a fasting blood glucose level that is higher than normal, yet not high enough to meet the criteria for type 2 diabetes. Patients with fasting plasma glucose levels between 100 mg/dL and 126 mg/dL are classified as having prediabetes, while patients with fasting plasma glucose levels of 126 mg/dL or higher are classified as having diabetes.1-3 Insulin resistance is a clinical feature of prediabetes and diabetes, not a separate clinical condition.
Twelve million adults in the United States have type 2 diabetes, but approximately 50% are undiagnosed. In addition, 41 million people ages 40 to 74 have prediabetes. Without treatment, hyperglycemia can have destructive microvascular and macrovascular effects on body tissues — all without producing symptoms. Considering the magnitude of this problem, screening for prediabetes during routine exams, health physicals and preventive health visits may be a cost-effective way for nurse practitioners to identify patients at risk.4 This identification paves the way for early intervention that can potentially alter the course of disease.
Microvascular Complications
A study that compared 5,431 diabetes patients from Wisconsin with 1,085 diabetes patients from Australia found that 21% of Wisconsin patients and 10% of Australian patients had retinopathy at the time they were diagnosed with type 2 diabetes.5 The study results indicate that retinopathy may appear 4 to 7 years before type 2 diabetes is diagnosed.
These researchers compared their results with a similar study that evaluated 240 men using the oral glucose tolerance test (OGTT) over a 10-year period.6 This study, conducted in England, revealed no retinopathy in the 160 men with prediabetes. But signs of retinopathy developed 5 years after type 2 diabetes diagnosis. Based on the findings of the two studies, the U.S. researchers suggested that type 2 diabetes may be undiagnosed for 9 to 12 years. As a result, microvascular and macrovascular complications may start much earlier in the prediabetes phase of the disease.5,7
Macrovascular Complications
The second National Health and Nutrition Examination Survey found that 22% of patients newly diagnosed with type 2 diabetes had cardiovascular abnormalities. Specifically, 10% experienced angina, 8% had peripheral vascular disease, and 6% experienced stroke.5 Clearly, undiagnosed diabetes is not benign. These findings and complications point to the need to screen for prediabetes and to intervene.
Risk Factors
Target prediabetes by taking aim at risk factors.2,8 In addition to elevated blood glucose, risk factors for prediabetes include advancing age, excess body fat, elevated lipid levels and personal or family history of altered carbohydrate metabolism (see table).
Visceral fat, like abdominal fat, has been linked to insulin resistance that hastens the onset of type 2 diabetes.9 Women tend to carry more body fat in the femoral and hip areas, which is less of a risk factor for type 2 diabetes than carrying fat in the abdominal and trunk area. Men tend to carry adipose tissue more centrally — a primary reason why men are at higher risk for prediabetes. Postmenopause status and certain body habitus types can also cause central adiposity in women.
Although men tend to have more abdominal fat, it is important to note the pattern of obesity in all patients, no matter what their sex.
Advancing age is another risk factor for prediabetes. All patients 45 and older should be screened for prediabetes every 3 years. Younger patients should be screened when other risk factors exist.2 Increasing age is associated with a decrease in beta cell function. In addition, age and increased abdominal fat are strongly associated with type 2 diabetes.10 Remember: Screening should be initiated whenever risk factors are present, no matter what the patient's age.4
Race and Ethnicity
Factors such as genetics, environment, diet, socioeconomic status and social influences may explain the racial and ethnic differences in type 2 diabetes. A study of 22 black and 22 Caucasian children in the United States analyzed the relationship of insulin clearance and insulin secretion to insulin sensitivity.10 The findings suggest that hyperinsulinemia in black children is related to lower insulin clearance levels than in white children. A metabolic difference in ethnicity may exist, along with a genetic component. In another recent study, researchers compared 53 black patients with 73 European Americans by genotyping to find a genetic component that may explain hyperinsulinemia among blacks.11,12 The study determined that blacks have higher fasting insulin levels than European Americans, supporting the possibility of genetic differences in carbohydrate metabolism.11,12
United States data show that compared with Caucasians, type 2 diabetes is two to six times more prevalent in people of African American, Native American, Pima Indian and Hispanic descent.13 Given these differences in ethnicity, it is imperative to modify other diabetes risk factors. The primary modifiable risk factors are activity, diet and obesity.
Lifestyle and Activity
A sedentary lifestyle slows glucose metabolism. Over time, this potentially increases body mass index (BMI). An elevated BMI is linked with insulin resistance. Physical activity increases insulin sensitivity and improves glucose metabolism by spurring insulin-receptor upregulation, which increases insulin and glucose delivery to muscles and tissues. A study evaluated whether increasing physical activity levels would reduce the risk of diabetes in women. The researchers found that BMI and physical activity were significant predictors of type 2 diabetes.13 Increased physical activity in the form of walking resulted in a modest reduction in diabetes risk. Reducing BMI had greater influence on the development of diabetes than physical activity alone. Thus, a combination of weight loss and increased physical activity is necessary to reduce type 2 diabetes risk.14
Obesity
Excess weight increases type 2 diabetes risk and increases the incidence of cardiovascular disease, hypertension, stroke, dyslipidemia and some cancers.15 Patients with a BMI of greater than 25 are categorized as overweight, and patients with a BMI of greater than 30 are categorized as obese. Using these BMI criteria, researchers identified an increasing prevalence of disease with obesity, including type 2 diabetes. These findings are consistent across ethnic groupings of men and women, including non-Hispanic whites, non-Hispanic blacks and Mexicans. Thus, it is relevant to screen patients across ethnic origins. The authors of this study recommended attentive efforts to identify and treat overweight adults before they become obese. Without such intervention, the health care system may be overwhelmed with obesity-related conditions.15
Another way to identify obesity in adults is waist circumference ratio. BMI reflects overall obesity, but waist circumference ratio is a predictor of abdominal obesity, a diabetes risk factor.8,16 BMI and waist-hip ratio indicate relative risk and the need to institute intervention for weight loss to reduce prediabetes and other pathologies. Waist measurements of more than 40 inches in men and more than 35 inches in women are considered risk factors for diabetes. A waist measurement that is larger than a hip measurement indicates abdominal obesity. Abdominal obesity in patients with insulin resistance may cause metabolic deterioration of insulin, resulting in hyperinsulinemia.9 Increased BMI and high waist-hip ratio are risk factors for insulin resistance, dyslipidemia and hypertension in addition to prediabetes.17
High Triglyceride Levels
Elevated triglyceride levels are more common in overweight men with high levels of visceral or abdominal fat. Visceral adipose tissue decreases the metabolic activity of lipids and lipoproteins, which increases cardiovascular disease.9 An elevated triglyceride level (more than 150 mg/dL) and increased abdominal obesity are part of the insulin resistance cascade, which may accelerate the development of type 2 diabetes.3
Patient History
A thorough patient history helps identify risk factors for prediabetes. A published review of studies that followed patients with a family history of diabetes, identical twins and women who had experienced gestational diabetes found the following:2,13
Thirty-nine percent of patients with type 2 diabetes have at least one parent with the disease.
Among identical twins with one affected twin, the unaffected twin has a 60% to 90% chance of developing type 2 diabetes.
Women who have experienced gestational diabetes during pregnancy or delivered an infant weighing more than 4 kilograms are at increased risk for type 2 diabetes.
Each of the risk factors listed above may be independent of the others, but the joint relationships among risk factors increase type 2 diabetes risk. Six prospective studies analyzed risk factors that may predict the progression from prediabetes to type 2 diabetes.18 These analyses clarified that fasting plasma glucose and BMI measurement were the most consistent and strongest predictors of the progression to type 2 diabetes.
Plan of Care
Recognition of clinical presentations and risk factors related to type 2 diabetes is essential. Screening for prediabetes evaluates the possibility of several clinical conditions, including obesity, hypertension and dyslipidemia. Screening can begin in the waiting room or in a patient-provider interview using a risk factor questionnaire prior to examination.
The table accompanying this article lists the five primary risk factors for prediabetes. The American Diabetes Association developed a questionnaire that assesses for these risk factors.1,2 It has demonstrated 79% sensitivity, 65% specificity and 10% positive predictive value for detecting prediabetes.1,2
If risk factors are present, further laboratory screening is necessary. Alone, the questionnaire or interview process provides educational information and awareness for the patient and provider. A complete screening for prediabetes includes identification of the five risk factors and correlation with laboratory values.4
Laboratory Screening
Fasting plasma glucose is a simple, cost effective screening tool for prediabetes. It is more widely used than the oral glucose tolerance test. The generally accepted criterion for diagnosing prediabetes is a result of 100 mg/dL to 126 mg/dL. The oral glucose tolerance test and the hemoglobin A1C, another measure of blood glucose, are not indicated for screening.1,19
The World Health Organization (WHO) and the ADA differ on the criteria for diabetes and hyperglycemia. The ADA recommends using only fasting plasma glucose, whereas the WHO recommends both fasting plasma glucose and the oral glucose tolerance test to make the definitive diagnosis of type 2 diabetes.20 In practice, fasting plasma glucose alone provides considerable information about the screening process and is cost effective.21
Intervention
For the patient diagnosed with prediabetes, significant lifestyle change is necessary. Research shows that patients who receive intensive individualized instruction about weight reduction, food intake and physical activity are better able to delay type 2 diabetes than control groups and patients who receive only brief counseling.
One of the largest diabetes prevention studies was a controlled clinical trial of 110,660 men and women from 33 health clinics in China. This randomized trial studied intensive diet and exercise and documented a 33% reduction in type 2 diabetes in the diet group, a 47% reduction in the exercise group, and a 38% reduction in the group that combined diet and exercise.22 The dieting and exercise that took place over the 6-year study was extensive. Patients received individual and group counseling weekly for 1 month, monthly for 3 months and then once every 3 months for the remainder of the study.
A 4-year study randomized 522 obese midlife adults (mean age 55 and mean BMI 31) to various intervention groups. The groups received individual counseling with detailed advice on reducing dietary fat and increasing fiber and physical activity. The intervention group received seven sessions during the first year and one session every 3 months thereafter. The overall incidence of diabetes decreased by 58%, and researchers determined the decrease was directly related to lifestyle modification. Other intervention studies highlight how effective lifestyle modification can be in preventing type 2 diabetes.22,23
This research draws attention to the high level of intervention required to reduce type 2 diabetes. It is our responsibility to provide necessary services or referrals for all patients who have prediabetes or are at risk for it. These patients require nutritional counseling and guidance about physical activity.21 Some experts believe that the growing epidemic of diabetes warrants intensive individualized counseling and guidance on a weekly or biweekly basis for a minimum of 1 month, and then every 3 months for the first year.21
Implications
Routine health encounters in primary care settings present a cost-effective opportunity for screening. All patients 45 and older should be routinely screened for diabetes.2 Intervention for patients at risk should include referral to knowledgeable and adequately trained nutritionists, dietitians, diabetes educators and fitness professionals who can help them achieve behavioral lifestyle changes.1
Case Example
Grace, a 47-year-old non-Hispanic woman, presents for an annual physical exam. At this office visit, she undergoes a blood draw to collect a fasting lipid profile and a fasting plasma glucose reading. Her height, weight, age and vital signs are collected for her annual physical in addition to the physical examination.
The physical exam reveals a BMI of 26 and a blood pressure of 130/86 mm Hg. Laboratory data reveal a fasting plasma glucose of 121 mg/dL and triglycerides of 295 mg/dL. Grace has four of the five risk factors for prediabetes: She is overweight and older than 45, and she has elevated lipid levels and borderline hypertension.
Interventions in this case include immediate lifestyle changes as well as thorough patient education about her increased risk for type 2 diabetes. In addition, Grace also requires a frank discussion of the asymptomatic microvascular and macrovascular complications that may already be taking place in her body and the likely progression of disease if she does not make lifestyle changes.
Putting It Into Practice
Elevated glucose levels may not produce symptoms for several years, meaning that significant vascular changes are likely to have occurred by the time the average patient is diagnosed with type 2 diabetes. Although it is well known that abnormal insulin secretion precedes insulin resistance, screening for prediabetes has not been incorporated into routine primary care practice. Nurse practitioners are qualified to alter this course, and we possess the diagnostic and patient education skills to make a dramatic positive impact on the prevention of type 2 diabetes.
References
1. American Diabetes Association. The prevention or delay of type 2 diabetes. Diabetes Care. 2002;25:742-749.
2. American Diabetes Association. Pre-diabetes. Available at: http://www.diabetes.org/pre-diabetes.jsp. Accessed Aug. 17, 2007.
3. Meigs JB. The metabolic syndrome (insulin resistance syndrome or syndrome X). Up to Date. Available with paid subscription at: www.utdol.com. 2005;13(2). Accessed Aug. 17, 2007.
4. Engelgau M, et al. Screening for type 2 diabetes. Diabetes Care. 2000;23(10):1563-1580.
5. Harris M, et al. Onset of NIDDM occurs at least 4 to 7 years before clinical diagnosis. Diabetes Care. 1992;15(7):815-819.
6. Jarret RJ. Duration of non-insulin dependent diabetes and development of retinopathy: analysis of possible risk factors. Diabetic Med. 1986;3:261-63.
7. Kanaya AM, et al. Predicting the development of diabetes in older adults: the derivation and validation of a prediction rule. Diabetes Care. 2005;28(2):404-408.
8. Lemieux S. Contribution of visceral obesity to insulin resistance syndrome. Can J Applied Physiol. 2001;26:273-290.
9. Utzschneider KM, et al. Impact of intra-abdominal fat and age on insulin sensitivity and beta-cell function. Diabetes. 2004;53(11):2867-2872.
10. Arslanian SA, et al. Hyperinsulinemia in African-American children: decreased insulin clearance and increased insulin clearance and its relationship to insulin sensitivity. Diabetes. 2002;51:3014-3019.
11. Gower BA, et al. Using genetic admixture to explain racial differences in insulin-related phenotypes. Diabetes. 2003;52(4):1047-1051.
12. McCulloch DK, Robertson RP. Prediction and prevention of type 2 diabetes mellitus. Up to Date. Available with paid subscription at: www.utdol.com. 2005;13(2). Accessed Aug. 17, 2007.
13. Weinstein AR, et al. Relationship of physical activity vs. body mass index with type 2 diabetes in women. JAMA. 2004;292(10):1188-1194.
14. Must A, et al. The disease burden associated with overweight and obesity. JAMA. 1999;282(16):1523-1529.
15. Gallagher D, et al. How useful is body mass index for comparison of body fatness across age, sex, and ethnic groups? Am J Epidemiol. 1996;143(3):228-239.
16. Ferreira I, et al. Development of fatness, fitness, and lifestyle from adolescence to the age of 36 years: determinants of metabolic syndrome in young adults: the Amsterdam Growth and Health Longitudinal Study. Arch Intern Med. 2005;165(1):42-48.
17. Edelstein SL, et al. Predictors of progression from impaired glucose tolerance to NIDDM: an analysis of six prospective studies. Diabetes. 1997;46(4):701-710.
18. Stern MP, et al. Identification of persons at high risk for type 2 diabetes mellitus: do we need the oral glucose tolerance test? Ann Intern Med. 2002;136(8):575-581.
19. Stolk RP, Orchard TJ. Why use the oral glucose tolerance test? Diabetes Care. 1995;18(7):1045-1049.
20. Gabir M, et al. The 1997 American Diabetes Association and 1999 World Health Organization criteria for hyperglycemia in the diagnosis and prediction of diabetes. Diabetes Care. 2000;23(8):1108-1112.
21. Pan XR, et al. The effects of diet and exercise in preventing NIDDM in people with impaired glucose tolerance. Diabetes Care. 1997;20(4):537-544.
22. Toumilehto J, et al. Prevention of type 2 diabetes mellitus by changes in lifestyle among subject with impaired glucose tolerance. N Engl J Med. 2001;344(18):1343-1350.
23. The Diabetes Prevention Research Group: Reduction in the evidence of type 2 diabetes with life-style intervention or metformin. N Engl J Med. 2002;346:393-403.
Carey Marie Boehm is a family nurse practitioner at Sacred Heart Hospital in Eau Claire, Wis. Sheila Smith is a family nurse practitioner with a PhD who is a professor and assistant dean of the College of Nursing and Health Sciences at the University of Wisconsin in Eau Claire.
Risk Factors for Prediabetes
Age older than 45
Fasting plasma glucose of 126 mg/dL or higher
BMI of 25 or higher
Triglyceride level of 150 mg/dL or higher
Family or personal history of glucose intolerance, gestational diabetes or birth of infant weighing more than 4 kilograms
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