Recommendation grades [A-E] and levels of evidence [I, II-1, II-2, II-3, III, good, fair, poor] are indicated after each recommendation. Definitions for these grades and levels are provided at the end of the "Major Recommendations" field.
The Canadian Task Force on Preventive Health Care (CTFPHC) concludes that there is fair evidence to recommend screening patients with hypertension for type 2 diabetes to reduce the incidence of cardiovascular (CV) events and CV mortality (B recommendation). (Harris & Eastman, 1998 [I, fair]; UK Prospective Diabetes Study (UKPDS) 38, 1998 [I, fair]; Schrier et al., 2002 [I, fair]; Estacio et al., 2000 [I, fair])
The CTFPHC concludes that there is fair evidence to recommend screening patients with hyperlipidemia for type 2 diabetes to reduce the incidence of CV events (B recommendation). (Pyorala et al., 1997 [I, good]; Koskinen et al., 1992 [I, good]; Frick et al., 1987 [I, good]; "Prevention of cardiovascular events," 1998 [I, good]; Downs et al., 1998 [I, good]; Rubins et al., 1999 [I, good]; Haffner et al., 1999 [I, good]; Pignone et al., 2001 [I, good]; MRC/BHF Heart Protection Study, 2002 [I, good]; Robins, 2001 [I, good]; Goldberg et al., 1998 [I, good])
The CTFPHC concludes that there is good evidence to recommend treatment of impaired glucose tolerance (IGT) with lifestyle interventions to reduce the incidence of diabetes progression (B recommendation). (Pan et al., 1997 [I, good]; Tuomilehto et al., 2001 [I, good]; Knowler et al., 2002 [I, good])
The CTFPHC concludes that there is insufficient evidence to recommend treatment of IGT with metformin or acarbose to reduce the incidence of diabetes progression (I recommendation). (Chiasson et al., 2002 [I, fair]; Knowler et al., 2002 [I, fair]; Diabetes Prevention Program Research Group, 2003 [I, fair])
The CTFPHC concludes that there is fair evidence to recommend treatment of IGT with acarbose to prevent CV events or hypertension (B recommendation). (Chiasson et al., 2003 [I, fair])
Clinical Considerations
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). 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.
Definitions:
Levels of Evidence
Research Design Rating
I: Evidence from randomized controlled trial(s)
II-1: Evidence from controlled trial(s) without randomization
II-2: Evidence from cohort or case-control analytic studies, preferably from more than one centre or research group
II-3: Evidence from comparisons between times or places with or without the intervention; dramatic results in uncontrolled studies could be included here
III: Opinions of respected authorities, based on clinical experience; descriptive studies or reports of expert committees
Quality Rating
Good: A study (including meta-analyses or systematic reviews) that meets all design- specific criteria* well
Fair: A study (including meta-analyses or systematic reviews) that does not meet (or it is not clear that it meets) at least one design-specific criterion* but has no known "fatal flaw"
Poor: A study (including meta-analyses or systematic reviews) that has at least one design-specific* "fatal flaw", or an accumulation of lesser flaws to the extent that the results of the study are not deemed able to inform recommendations
*General design-specific criteria are outlined in Harris RP, Helfand M, Woolf SH, Lohr KN, Mulrow CD, Teutsch SM, Atkins D. Current Methods of the U.S. Preventive Services Task Force: A Review of the Process. Am J Prev Med 2001;20(suppl 3):21-35.
Recommendations Grades for Specific Clinical Preventive Actions
A: The Canadian Task Force (CTF) concludes that there is good evidence to recommend the clinical preventive action.
B: The CTF concludes that there is fair evidence to recommend the clinical preventive action.
C: The CTF concludes that the existing evidence is conflicting and does not allow making a recommendation for or against use of the clinical preventive action; however, other factors may influence decision-making.
D: The CTF concludes that there is fair evidence to recommend against the clinical preventive action.
E: The CTF concludes that there is good evidence to recommend against the clinical preventive action.
I: The CTF concludes that there is insufficient evidence (in quantity and/or quality) to make a recommendation; however, other factors may influence decision-making.
