DOI: 10.2337/dc07-1574
Isolated Impaired Fasting Glucose and Peripheral Insulin Sensitivity: Not a Simple RelationshipDepartment of Medicine, Stanford University School of Medicine, Stanford, CA sunhkim{at}stanford.edu ABSTRACT Objective: In a recent consensus statement, the American Diabetes Association (ADA) concluded that individuals with impaired fasting glucose (IFG) have "normal muscle insulin sensitivity." To subject this conclusion to further validation, we evaluated the relationship between glucose tolerance categories and peripheral insulin sensitivity in a large nondiabetic population. Research Design and Methods: Insulin sensitivity was directly quantified by determining the steady-state plasma glucose (SSPG) concentration during the insulin suppression test in 446 nondiabetic individuals, divided into four groups: normal glucose tolerance (NGT, n=318), isolated IFG (n=63), isolated impaired glucose tolerance (IGT, n=33), and combined IFG and IGT (IFG/IGT) (n=32). Results: Insulin sensitivity was significantly different in all three groups with prediabetes (IFG, IGT, IFG/IGT) as compared with NGT (p<0.05). Using tertiles of SSPG concentration in the NGT group as operational definitions of insulin resistance (highest tertile) and insulin sensitivity (lowest tertile), there was considerable heterogeneity within the prediabetic groups. Thus, 57% of IFG individuals were insulin resistant, and 13% were insulin sensitive. The IFG/IGT group was most homogeneous with 94% classified as insulin resistant and only 3% as insulin sensitive. Conclusions: Peripheral insulin sensitivity varies considerably in nondiabetic individuals with IFG individuals showing the most heterogeneity within the prediabetes group. We believe that this heterogeneity in insulin sensitivity, and the relatively few patients in whom insulin sensitivity has been measured directly in the past, explain the discrepancy between our findings and the recent consensus statement by the ADA.
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