The American Diabetes Association (ADA) estimates that as many as 5.2 million of the 18.2 million Americans who have diabetes mellitus don't know they do.1 For as many as possible to be diagnosed and treated, it's important that health care providers identify and screen those at high risk for diabetes. Intuitively, that approach makes sense. After all, damage to the eyes, kidneys, nerves, heart, and blood vessels are well-known consequences of chronic hyperglycemia. To make matters worse, most newly diagnosed type 2 diabetes patients have had the disease for as long as 10 years without treatment and have therefore been at risk for serious complications prior to diagnosis. 2 But are there data that support screening asymptomatic people?
Recently, the U.S. Preventive Services Task Force (USPSTF) updated its 1996 recommendations concerning screening for type 2 diabetes in adults, concluding that although there was sufficient evidence to support the screening of those with hypertension (to reduce the incidence of cardiovascular events) and hyperlipidemia (to reduce the risk of coronary heart disease), the evidence supporting the screening of otherwise asymptomatic adults was insufficient.
I have serious concerns about these recommendations further delaying diagnosis in millions of Americans. One of the reasons there are so many people unaware that they have diabetes is that they either are asymptomatic or don't recognize the symptoms. Type 2 diabetes is a disease of both insulin resistance and insulin deficiency that, generally, takes many years to develop. Most patients with diabetes are obese, contributing further to insulin resistance. It falls to both clinician and patient to decide whether screening for type 2 diabetes should be performed. The USPSTF recognizes that physical inactivity, dietary habits, and excessive weight may pose a greater risk of having diabetes and should be considered as factors in screening for the disease. While these are indeed significant, the ADA recommends the consideration of additional risk factors such as age of more than 45 years, a history of gestational diabetes, the bearing of a child weighing more than 9 lbs., a history of polycystic ovary syndrome, a history of vascular disease, race (African Amer-ican, Hispanic, Native American, Asian American, or Pacific Islander), and diagnosis in a first-degree relative.
The ADA and the USPSTF agree that changes in lifestyle, especially diet and exercise, should be initiated as soon as possible after clinical diagnosis.
According to the ADA, people with a high risk of having diabetes mellitus should be screened for it according to the following diagnostic criteria in any combination of any two of the following on two separate days: a random plasma glucose level greater than or equal to 200 mg/dL with symptoms (polyuria, polydipsia, and inexplicable loss of weight), a fasting plasma glucose (FPG) level greater than or equal to 126 mg/dL or a two-hour postload (75-g anhydrous) glucose level greater than or equal to 200 mg/dL. The glycosylated hemoglobin (HbAIc) test, which reflects a two-month average blood sugar level, is not recommended as a screening test by either the ADA or the USPSTF, mostly, according to the USPSTF, because of the lack of national standardization and because it's less sensitive in detecting lower levels of hyperglycemia at the usual cutpoints. The ADA diagnostic criteria are based on evidence that high glucose levels, as determined by the FPG and two-hour post-load glucose tests, have been associated with serious complications of diabetes necessitating intervention. The ADA and the USPSTF agree that changes in lifestyle, especially diet and exercise, should be initiated as soon as possible after clinical diagnosis, and the USPSTF cites in its updated recommendations three recent randomized, controlled trials conducted in China, Finland, and the United States in which the incidence of type 2 diabetes in people at high risk for developing the disease was reduced by as much as 58% through modifications in lifestyle.
The USPSTF examined various complications of diabetes to determine whether early intervention would be worthwhile. Although there was evidence that early intervention might delay the progression of serious microvascular complications, there was no evidence to suggest that early intervention between screening for diabetes and clinical diagnosis of retinopathy, chronic renal failure, or lower extremity amputation would have a significant impact on the development of those complications. The USPSTF panel cites studies supporting and its recommendation that only people with hypertension or hyperlipidemia, or both, should be screened for diabetes.
The USPSTF tries to justify its relaxed diabetes screening recommendations in an expression of concern with the "labeling" of asymptomatic patients as having diabetes and the anticipation of their difficulties in obtaining health insurance coverage if incorrectly diagnosed because of a false-positive result of a screening test with poor sensitivity. At the same time it concedes that there is little evidence that such "labeling" occurs as a result of such screenings. In addition, the USPSTF expresses concern that false-positive screenings can cause unnecessary psychological distress.
Because type 2 diabetes is chronic, progressive, and manageable, I support the ADA's recommendations for screening. I wouldn't want to risk missing a diagnosis and delaying treatment because of a simple blood test. I recently participated in a community health fair at which the ADA diabetes risk assessment and blood testing were offered. If participants answered any screening questions affirmatively, they received counseling in lifestyle modification, and if they scored 10 or higher on the assessment questionnaire, a blood test also was offered. (An HbAIc test was performed by a laboratory technician and I reviewed the results with the participant. Although use of the test for screening is controversial, it's convenient and may represent a reasonable approach. 3 I have found that it has an advantage in that it reflects a two-month average blood sugar level and the participant need not be questioned about recent dietary intake. Moreover, Sacks, in the American Association for Clinical Chemistry guidelines for diagnosis and management of diabetes asserts that further studies to determine whether the HbAIc test is a useful screening tool are necessary. 4)
Although the USPSTF would probably discourage such public community screening in which risk is not assessed according to blood pressure or lipid levels exclusively, I found it to be extremely useful, because it afforded me the opportunity to counsel people at high risk and, it's hoped, to motivate them to begin making improvements in diet and level of physical activity. Participants already diagnosed with diabetes came to the informal screening seeking guidance, and we offered both the blood test and counseling in the importance of a proper diet, exercise, and regular visits to a primary care provider.
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