2270-P: Glucose Dynamic Instability on Continuous Glucose Monitoring Discriminates Cystic Fibrosis–Related Diabetes

Introduction and Objective: Cystic fibrosis-related diabetes (CFRD) is associated with adverse clinical outcomes, yet early metabolic dysregulation may be inadequately captured by conventional glycemic markers. Continuous glucose monitoring (CGM) enables assessment of glucose dynamics. We evaluated whether a CGM-derived Poincaré plot (PP) ellipse area (S), a measure of glucose dynamic instability, discriminates glycemic status in adults with cystic fibrosis. Methods: In a prospective observational cohort, adults with cystic fibrosis underwent CGM and HbA1c assessment at 2-3 structured study visits conducted within the same year. Participants with insufficient CGM data (<70% active CGM) or missing CGM were excluded, yielding 67 individuals for analysis (NGT n=19, AGT n=21, CFRD n=27). S was computed from CGM time series. Diagnostic performance was evaluated using receiver operating characteristic (ROC) analysis, with optimal thresholds selected using the Youden index. Results: Median S increased progressively across glycemic categories (NGT: 627; AGT: 908; CFRD: 1941 mg²/dL²). Discrimination of CFRD versus NGT was excellent (AUC 0.95; 95% CI 0.89-1.00), with 85% sensitivity and 100% specificity at the optimal cutoff (S≈1260 mg²/dL²). For CFRD versus non-CFRD, S demonstrated strong performance (AUC 0.90; 95% CI 0.82-0.98), with 85% sensitivity, 90% specificity, and a negative predictive value of 90%. Discrimination of AGT versus NGT was moderate (AUC 0.74; 95% CI 0.59-0.90). Conclusion: A novel CGM-derived measure of glucose dynamic instability robustly discriminates CFRD and may provide a clinically meaningful tool for early detection and risk stratification beyond conventional glycemic indices. Disclosure E. Montaser: None. M.S. Putman: Advisory Panel; Current; Vertex Pharmaceuticals Incorporated. Research Support; Ended; Vertex Pharmaceuticals Incorporated, Dexcom, Inc. Advisory Panel; Ended; Sanofi. Board Member; Current; Anagram Therapeutics. Research Support; Ended; Samsung. V. Shah: Advisory Panel; Current; Abbott Diabetes, Dexcom, Inc. Advisory Panel; Ended; Medtronic. Advisory Panel; Current; Novo Nordisk, Eli Lilly and Company. Consultant; Current; Insulet Corporation, T1D Exchange. Advisory Panel; Current; Sanofi, Tandem Diabetes Care, Inc. Consultant; Ended; DreaMed Diabetes, Ltd.