Type 2 Diabetes Screening Guidelines Updated

Laurie Barclay, MD

October 18, 2012

Routine screening for type 2 diabetes is recommended for asymptomatic adults at high to very high risk, but not for those at low to moderate risk, according to updated guidelines from the Canadian Task Force on Preventive Health Care (CTFPHC). This update to the 2005 CTFPHC recommendations targets clinicians as well as those involved in healthcare policy and is published in the October 16 issue of the Canadian Medical Association Journal.

"These new guidelines bring precision and convenience with web-based risk calculators and nonfasting A1C to diabetes screening," guidelines author Kevin Pottie, MD, from the Department of Family Medicine, University of Ottawa, Ontario, Canada, said in a journal news release. "Leveraging these tools will help improve health outcomes by empowering patients to take an active role in managing and modifying their own risk factors through interventions like diet and exercise."

Prevalence of confirmed type 1 or type 2 diabetes among Canadians was about 2.4 million (6.8% of the population) in 2008 to 2009, and estimated prevalence of undiagnosed diabetes was 480,000 (1.4%). Health policy experts anticipate significant increases in diabetes prevalence during the next decade, with attendant comorbidity including vascular disease.

The CTFPHC, an independent body of 14 experts in primary care and prevention convened by the Public Health Agency of Canada, reviewed findings of a large randomized trial and other recent studies. These data offered no evidence that screening for type 2 diabetes in adults younger than 40 years who are at low to moderate risk for diabetes lowers the incidence, mortality, or complications of diabetes.

However, some evidence suggests that screening adults at high or very high risk for diabetes may lower rates of myocardial infarction, microvascular complications, and mortality.

"The guidelines highlight the need to focus on people at high and very high risk as prevalence rates of diabetes increase," the task force noted in the news release. "Even in this group there is little evidence that frequent screening is beneficial, especially for reducing mortality."

Nonfasting A1C is the recommended screening test, which will allow clinicians to use the same test for screening and monitoring and may improve patient compliance by eliminating the need for fasting.

Key Recommendations

  • To assess risk level among the general population, use a validated risk calculator rather than a routine blood test for the first stage of screening.

  • The preferred screening tool is the Finnish Diabetes Risk Score (FINDRISC), although the Canadian Diabetes Risk Assessment Questionnaire (CANRISK) is an acceptable alternative. These validated risk calculators may also educate patients about their risk factors.

  • FINDRISC and CANRISK assign risk values based on age, obesity, history of hyperglycemia, history of hypertension, family history of diabetes, limited activity levels, and limited dietary intake of fruits and vegetables.

  • The preferred blood test for screening is A1C, although fasting glucose measurement and the oral glucose tolerance test are acceptable alternatives.

  • The recommended threshold for diagnosing diabetes is an A1C level of at least 6.5%, but lower values do not exclude diabetes diagnosed with glucose tests. A1C should be measured with a standardized, validated assay.

  • Do not perform routine blood test screening on asymptomatic adults younger than 40 years, except for those at high or very high risk for diabetes. This is a weak recommendation based on low-quality evidence.

  • Perform A1C blood test screening every 3 to 5 years among adults who are at least 40 years of age and at low to moderate risk and among those at high risk at any age. This is a weak recommendation based on low-quality evidence.

  • Perform A1C blood test screening annually among adults of any age who are at very high risk for diabetes. This is a weak recommendation based on low-quality evidence.

"There was no evidence to support routine screening with a blood test for type 2 diabetes among adults at low or moderate risk of diabetes," the task force concluded in the news release. "Screening this population may lead to overdiagnosis, inappropriate investigation and treatment, and unnecessary psychosocial and economic costs."

One author received a research grant from sanofi-aventis for an economic analysis of an office-based care model for patients with type 2 diabetes. The other guidelines authors have disclosed no relevant financial relationships.

CMAJ. 2012;184:1687-1696. Full text