Abstract Disclosure: D. Kim: None. S. Ryang: None. M. Im: None. J. Kim: None. Y. Kim: None. Y. kim: None. J. ha: None. J. Kim: None. S. Kim: None. Background and Aims: This study investigated the main factors responsible for the differences between blood glucose (BG) and interstitial fluid glucose (ISF) during glucose loading. Methods: A total of 204 Korean subjects without history of type 2 diabetes were enrolled. The subjects were categorized into three groups according to diabetes criteria by American Diabetes Association; NGT (normal glucose tolerance, n=36), PreDM (prediabetes, n=130) and T2D (undiagnosed type 2 diabetes, n=38). For glucose monitoring, a CGM (continuous glucose monitoring) system (Dexcom G6, Dexcom, San Diego, USA) was attached for 10 days. 75g oral glucose tolerance test (OGTT) was performed during applying CGM with stabilization (after wear of 3 days). Blood sample collected at t=0, 30, 60, 90 and 120 min for glucose and insulin concentration. Two parameters [insulin sensitivity (mIS) and beta-cell function (mBCF)] were derived novel mathematical model. Results: Among NGT, PreDM and T2D, there are heterogeneity in the difference and pattern between BG and ISF in this study. We identified the probability density function of BG - ISF across glucose tolerance, there is a trend that the means of BG - ISF with G60, 90, and 120 move to the right, as glucose tolerance status changes NGT to PreDM and DM. BG - ISF is significantly associated with insulin resistance (R=0.32, p<0.001), not diminished beta cell function. Conclusions: Because individuals vary in their degree of insulin resistance as a primary pathophysiology of type 2 diabetes, the caution should be needed in interpreting the glycemic response of CGM after a glucose load. Presentation: 6/3/2024