Full The Relationship between Continuous Glucose Monitoring and OGTT in Youth and Young Adults with Cystic Fibrosis
Abstract Context Early glucose abnormalities in people with CF (PwCF) are commonly detected by continuous glucose monitoring (CGM). Relationships between these CGM abnormalities and oral glucose tolerance testing (OGTT) in PwCF have not been fully characterized. Objective(s) 1) To determine the relationship between CGM and common OGTT-derived estimates of β-cell function, including C-peptide index and oral disposition index (oDI) and 2) to explore whether CGM can be used to screen for OGTT-defined prediabetes and cystic fibrosis related diabetes (CFRD). Study Design/Methods PwCF not on insulin and healthy controls ages 6-25 yrs were enrolled in a prospective study collecting OGTT and CGM. A subset underwent frequently-sampled OGTTs (fsOGTT) with 7-point glucose, insulin, and C-peptide measurements. Pearson’s correlation coefficient was used to test the association between select CGM and fsOGTT measures. ROC analysis was applied to CGM variables to determine the cutoff optimizing sensitivity and specificity for detecting prediabetes and CFRD. Results A total of 120 participants (controls=35, CF=85), including 69 with fsOGTTs, were included. CGM coefficient of variation correlated inversely with C-peptide index (Cpeptide30-Cpeptide0/Glucose30-Glucose0) (r=-0.45, p<0.001) and oDIcpeptide (C-peptide index)(1/cpep0) (r=-0.48, p<0.0001). In PwCF, CGM variables had ROC-AUCs ranging from 0.43-0.57 for prediabetes and 0.47-0.6 for CFRD. Conclusions Greater glycemic variability on CGM correlated with reduced β-cell function. However, CGM performed poorly at discriminating individuals with and without OGTT-defined CFRD and prediabetes. Prospective studies are now needed to determine how well the different tests predict clinically-relevant non-glycemic outcomes in PwCF.