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In developing these recommendations, the Canadian Task Force on Preventive Health Care drew heavily on a recent systematic review prepared for the US Preventive Services Task Force of the evidence for screening asymptomatic people for type 2 diabetes mellitus to prevent cardiovascular events.1 That review was enhanced by the Canadian Task Force on Preventive Health Care in 2 ways: all new literature on screening was incorporated, and a separate systematic review of the evidence related to the prevention of diabetes in people with impaired glucose tolerance was undertaken.
In patients who do not meet the above criteria, the decision to screen for diabetes or impaired glucose tolerance may be made on an individual basis. The decision to screen should hinge on an estimate of the patient's overall risk of cardiovascular disease (CVD). Patients whose overall risk would be raised by a diagnosis of diabetes to the extent that treatment would be changed (i.e., if the overall risk of CVD is raised to more than 10%) may merit screening. Patients with other known CVD risk factors (e.g., smoking or increased age) may also benefit from screening for diabetes.
Screening involves only patients who are asymptomatic. Those who exhibit symptoms or signs of diabetes, or those who have potential complications associated with diabetes, should receive diagnostic testing.
Screening is best accomplished with a fasting plasma glucose test. Diabetes is diagnosed if the fasting plasma glucose level is 7.0 mmol/L or greater, or if the plasma glucose level is 11.1 mmol/L or greater in a 2-hour oral glucose tolerance test (OGTT).2 Either test should be done on 2 occasions before a diagnosis can be made. Impaired fasting glucose is diagnosed if the fasting glucose level is 6.1–6.9 mmol/L, and impaired glucose tolerance is diagnosed if the plasma glucose level is 7.8–11.0 mmol/L in a 2-hour OGTT.
There is no information regarding the optimal screening frequency.
In its 2003 clinical practice guidelines the Canadian Diabetes Association recommends screening for diabetes with a fasting plasma glucose test every 3 years in people 40 years of age and older (grade: consensus).3 It recommends that screening be considered at an earlier age or be performed more frequently, or both, using a fasting glucose or 2-hour OGTT in people with additional risk factors for diabetes (grade: consensus).3
The American Diabetes Association recommends that patients, particularly those with a body mass index of 25 kg/m2 or greater, be screened with a fasting glucose test every 3 years beginning at the age of 45 years.4 It, too, suggests that testing be considered at an earlier age or be carried out more frequently in people who are overweight if additional diabetes risk factors are present.
The US Preventive Services Task Force found the evidence insufficient to recommend for or against routine screening of asymptomatic adults for type 2 diabetes, impaired glucose tolerance or impaired fasting glucose (grade I recommendation).5 It does, however, recommend screening for diabetes in adults with hypertension or hyperlipidemia (grade B recommendation).
We thank Dr. Russell Harris for his valuable input and Ruth Walton for her helpful assistance in preparing this manuscript.
An abridged version of this article appeared in the Jan. 18, 2005, issue of CMAJ and is available online at www.cmaj.ca/cgi/content/full/172/2/177/DC1
Contributors: Denice Feig and Valerie Palda reviewed the systematic review prepared for the US Task Force on Preventive Health Care, updated the literature on screening and wrote the technical report on which this article is based. Lorraine Lipscombe conducted the systematic review of prevention of diabetes in individuals with impaired glucose tolerance and wrote sections of the technical report related to that topic. Denice Feig drafted the recommendation statement; Lorraine Lipscombe and Valerie Palda reviewed drafts and made subsequent revisions. The Canadian Task Force on Preventive Health Care critically reviewed the evidence and developed the recommendations according to its methodology and consensus development process.
The Canadian Task Force on Preventive Health Care is funded by Health Canada.
This statement is based on the technical report: “Screening for type 2 diabetes to prevent vascular complications: updated recommendations from the Canadian Task Force on Preventive Health Care,” by Denice Feig, Valerie A. Palda and Lorraine Lipscombe, with the Canadian Task Force on Preventive Health Care. The full technical report is available from the task force at gro.chpftc@ftc.
Competing interests: None declared for Valerie Palda or Lorraine Lipscombe. Denice Feig has received research funding from Novo Nordisk and an unrestricted educational grant from Aventis Pharma.
Correspondence to: Canadian Task Force on Preventive Health Care, 117–100 Collip Circle, London ON N6G 4X8; fax 519 858-5112; gro.chpftc@ftc