MON-596 Evaluation of Continuous Glucose Monitoring Thresholds for Diabetes Screening in Cystic Fibrosis: Insights from the EnVision-Glucose Tolerance Study

Abstract Disclosure: Z.V. Hurt: None. T. Vigers: None. A. Granados: None. A. Moheet: None. K. Larson Ode: None. C.L. Chan: None. Continuous glucose monitoring (CGM) is increasingly used in cystic fibrosis (CF) to aid cystic fibrosis related diabetes (CFRD) screening and clinical decision making. However, evidence based data to guide interpretation of CGM findings in this population are limited. A recent paper (Scully et al, JCEM, 2022) proposed CGM cutoffs of >17.5% time spent >140 mg/dL and >3.4% time >180 mg/dL for diagnosis of CFRD, finding them highly sensitive (87%, 90%) and specific (95% for both). We aimed to examine these thresholds in an independent cohort derived from the EnVision Multicenter Glucose Tolerance (EnVision-MGT) study (NCT: 03650712). EnVision-MGT is a 4 site multicenter study that enrolled people with CF ≥6 years from 2019-2023, without known diabetes. All participants underwent oral glucose tolerance testing (OGTT). CGM data was collected in a subset of participants. In this study, we included participants who had both CGM and OGTT results available. We then dichotomized participants by the CGM cutoffs proposed by Scully et al and compared OGTT results and hemoglobin A1c levels (HbA1c). Descriptive statistics were applied. Fischer’s exact and Wilcoxon rank sum tests were used to compare groups, and p<0.05 was considered significant. Continuous data are presented as median (IQR) and categorical data by N or percent. Data were available in 134 unique CF participants: 50% male, age = 17 [13,27] years. Based on fasting (FPG), 1 hour (1hG) and 2 hour (2hG) OGTT glucoses, 29% had normal glucose tolerance (NGT), 5.2% had impaired fasting glucose (IFG), 16% had indeterminant glucose tolerance (INDET), 49% had impaired glucose tolerance (IGT), and 0% had CFRD. Grouped by CGM time spent >140mg/dL, 12/134 (9%) participants had >17.5% time >140. Of these, 1=NGT, 1=INDET, and 10=IGT. Compared to those with <17.5% time spent >140 mg/dL, HbA1c was higher (5.7% (5.5, 6.3) vs. 5.5% (5.3, 5.7), p=0.008), FPG did not differ, 1hG was higher (245mg/dL (213, 273) vs 188mg/dL (154, 224), p=0.002), and 2hG was higher (184mg/dL (152, 230) vs 134mg/dL (101, 167), p=0.002). Grouped by CGM time spent >180mg/dL, 22/134 (16%) had >3.4% time >180 mg/dL. Of these, 4 (18%) had NGT, 4 (18%) had INDET and 14 (64%) had IGT. Compared to those with <3.4% time spent >180 mg/dL, HbA1c was higher (5.7% (5.4, 6.2) vs 5.5% (5.3, 5.7), p=0.029), and 1hG was higher (218mg/dL (190, 273) vs 187mg/dL (155, 224), p=0.011). There were no differences by FPG, and 2hG were not different (163mg/dL (110, 220) vs. 134mg/dL (103, 166), p=0.050). Nine and 16% of 134 people with CF without CFRD by OGTT criteria were classified as CFRD by Scully criteria, giving a specificity of 91 and 84%. These thresholds identified individuals with higher HbA1c, 1hG and/or 2hG on OGTT. However, CGM has not yet been linked to CF outcomes. Thus, prospective, longitudinal studies are still needed to determine whether CGM predicts clinical outcomes as well as, or better than, OGTT in people with CF. Presentation: Monday, July 14, 2025