Changing the definition of impaired fasting glucose: impact on the classification of individuals and risk definition.

OBJECTIVE: This study evaluates the impact of lowering the diagnostic threshold for impaired fasting glucose (IFG) from 6.1 to 5.6 mmol/l as proposed by the American Diabetes Association (ADA) on the prevalence of the condition, classification of individuals, and risk definition. RESEARCH DESIGN AND METHODS: A total of 1,285 employees of the Italian Telephone Company aged 35-59 years without known diabetes underwent an oral glucose tolerance test (OGTT). BMI, serum cholesterol, triglycerides, and blood pressure were measured. Medication use was recorded.
RESULTS: With the new ADA criterion, the proportion of people diagnosed with IFG increased from 3.2 to 9.7%. The newly proposed IFG category identified 41% of all subjects with impaired glucose tolerance (IGT) compared with 16.2% identified with the use of the World Health Organization criterion for IFG; the improvement in accuracy has been achieved at the cost of classifying more previously "normal" subjects as having IFG (from 2.3 to 7.3%). Both IFG and IGT were associated with an unfavorable risk profile for diabetes and cardiovascular disease, with a higher estimated risk for IGT than IFG.
CONCLUSIONS: Even with the revised diagnostic criterion, IFG and IGT identify distinct groups that have a different background risk. The cost/benefit of preventive measures tested in people with IGT may not apply to the new IFG category.