Impact of lowering the criterion for impaired fasting glucose on identification of individuals with insulin resistance. The GISIR database

OBJECTIVE: We assessed the accuracy of the American Diabetes Association (ADA)2003 definition of impaired fasting glucose (IFG) in identifying subjects with low insulin sensitivity, and determined cardiovascular risk factors in ADA2003 IFG subjects. RESEARCH DESIGN AND METHODS: This study included 930 non-diabetic Italian Caucasians from the GISIR database in which subjects underwent a hyperinsulinaemic-euglycaemic clamp performed with a standard technique. Low insulin sensitivity was defined as being in the lower quartile of glucose metabolized during the last hour of the clamp (M). Subjects were stratified in the following groups: normal fasting glucose (NFG) (<100 mg/dL), IFG100 (100-109 mg/dL), ADA1997 IFG110 (110-125 mg/dL), and ADA2003 IFG (100-125 mg/dL). RESULTS: The sensitivity of identifying subjects with low insulin sensitivity increased adopting the ADA2003 criterion. After Bonferroni correction for multiple comparisons, both IFG100 and ADA1997 IFG110 showed significantly higher body mass index (BMI), waist, systolic blood pressure (SBP) and diastolic blood pressure (DBP), triglyceride, fasting plasma insulin (FPI) and fasting plasma glucose (FPG), and lower insulin sensitivity as compared with NFG. As compared with IFG100, ADA1997 IFG110 showed significantly higher BMI, waist, SBP, FPI, FPG, and lower insulin sensitivity. ADA2003 IFG group showed significantly higher BMI, waist, SBP and DBP, triglyceride, cholesterol, FPI, and FPG, but lower HDL levels and insulin sensitivity compared with NFG subjects. CONCLUSIONS: Although neither the ADA2003 nor the ADA1997 definition of IFG appears to be particularly efficacious for the identification of subjects' low insulin sensitivity, lowering the criterion to the ADA2003 glucose threshold increased the sensitivity without affecting the specificity. ADA2003 IFG showed a worse cardiovascular risk profile compared with NFG.