Screening for Diabetes and Prediabetes in Cystic Fibrosis Using a Nonfasting 50-Gram 1-Hour Oral Glucose Challenge...

Cystic fibrosis (CF)-related diabetes (CFRD) affects nearly half of adults with CF, but screening rates with the recommended oral glucose tolerance test (OGTT) are low. We evaluated the utility of a nonfasting, 50-g, 1-h oral glucose challenge test (GCT) as first-line screening for CFRD and pre-CFRD. The objectives were to define a cutoff that provides high sensitivity and reasonable specificity, and to determine how GCT compares with other opportunistic tests.

Participants with CF ≥10 years old, without known diabetes, had baseline random plasma and capillary glucose (RPG and RCG), then underwent an in-clinic GCT for collection of 1-h plasma glucose (GCTpl). This was followed by hemoglobin A1C (HbA1c) and OGTT on a separate day. Receiver operating characteristic (ROC) curves were generated for identifying CFRD and pre-CFRD.

Of 185 participants, 94 had normal glucose tolerance, 81 had pre-CFRD, and 10 had CFRD. For detecting pre-CFRD or CFRD, GCTpl had an area under the ROC curve (ROC-AUC) of 0.73 (95% CI 0.65-0.80), higher than ROC-AUCs for RPG of 0.56 (0.48-0.65, P = 0.003), RCG of 0.55 (0.46 = 0.63, P = 0.002), and HbA1c of 0.62 (0.53-0.67, P = 0.02). The ROC-AUC for detecting CFRD was 0.75 (0.64-0.86) for GCTpl, 0.64 (0.42-0.87) for RPG, and 0.56 (0.39-0.73) for HbA1c. A GCTpl of 147 mg/dL provides 90% sensitivity and 58% specificity for detecting CFRD and could reduce the OGTTs needed by 56%.

GCT offers a practical, in-clinic method for CFRD screening. This spares low-risk individuals from OGTT, while maintaining high sensitivity for CFRD.