Continuous glucose monitoring abnormalities are present in the prediabetic state, but how these abnormalities compare among individuals at risk for different types of diabetes (type 1, type 2, vs. cystic fibrosis related diabetes) is unknown. We compared CGM patterns of three distinct groups of youth at risk for diabetes, all with A1c In conclusion, CGM patterns are significantly different in pre-T1D and CF compared to obese/pre-T2D, reflecting differences in pathophysiology among these disease states. Early insulin deficiency appears to manifest as greater glycemic variability—higher SD, greater peaks and lows—in pre-T1D and CF, while insulin resistance leads to increased, but less variable, glucoses in obese/preT2D youth. *pre-T1D and CF significantly different from pre-T2DCGM measure (sensor glucose) Mean (SE) (mg/dl)Pre-T1D (N=14)Pre-T2D (n=42)CF (n=42)P-valueAverage glucose117 (3)114 (2)111 (2)0.17Standard deviation (SD)26 (2)16 (1)22 (1)12037 (5)31 (4)27 (2)0.24% time 14017 (4)12 (3)9 (1)0.23% time >2001.3 (0.7)0.4 (0.2)0.8 (0.2)0.11 Disclosure C.L. Chan: None. A. Steck: None. T.B. Vigers: None. L. Pyle: None. F. Dong: None. J. Thurston: None. M. Rewers: None. P. Zeitler: Consultant; Self; Daiichi Sankyo Company, Limited, Merck & Co., Inc., Eli Lilly and Company, Takeda Development Center Americas, Inc., Boehringer Ingelheim GmbH. K.J. Nadeau: None.