P-221: High glycaemic variability in CGM data indicates early dysglycaemia in young people with cystic fibrosis: an OGTT-CGM comparison pilot study
A Felser, C De Jong, I Korten, C BoettcherAbstract
Introduction
Continuous glucose monitoring (CGM) is increasingly used to identify glucose abnormalities in young people with cystic fibrosis (pwCF).
Objectives
To identify which CGM-derived metrics best reflect early abnormalities detected by an oral glucose tolerance test (OGTT) in pwCF without CFRD.
Methods
We performed an exploratory analysis of 28 pwCF undergoing OGTT followed by CGM. OGTT categories were defined as normal glucose tolerance or abnormal OGTT, including isolated 60’ hyperglycaemia (>7.7 mmol/L), indeterminate glucose tolerance (INDET, 60’ ≥11.1 mmol/L, normal 120’ glucose), or impaired glucose tolerance (IGT, 120’ 7.8-11.0 mmol/L). CGM metrics comprised mean glucose, time >10 mmol/L, time >7.8 mmol/L, and coefficient of variation (CV). Sensitivity, specificity and discrimination were calculated by the area under the curve (AUC) in the receiver operator curve (ROC).
Results
The participant’s median age was 14 years (range 10-18). Mean fasting, 60’, and 120’ glucose was 4.8, 6.0, and 5.2 mmol/L in normal OGTT (n=9), and 5.2, 9.9, and 6.3 mmol/L in abnormal OGTT (n=19), respectively. Abnormal OGTT was mainly due to early abnormalities, such as isolated 60’ hyperglycaemia (n=13), INDET (n=4), and IGT (n=2). CGM showed a low overall hyperglycaemic burden in both, normal and abnormal OGTT groups: time >10 mmol/L (median 1% vs 2%), time >7.8 mmol/L (median 15% vs 12%) and mean glucose (median 6.5 vs 6.4 mmol/L). However, CV was higher in abnormal OGTT (median 17.8% vs 21.3%, p=0.01). In an ROC analysis, CV discriminated abnormal OGTT results with an AUC of 0.79 (CI 0.61-0.97), compared with AUCs of 0.57, 0.52, and 0.51 for time >10 mmol/L, >7.8 mmol/L, and mean glucose, respectively.
Conclusions
Early dysglycaemia in CGM is characterised by increased glycaemic variability rather than overt hyperglycaemia, indicating that glucose instability precedes measurable hyperglycaemia in CF. Variability-based CGM metrics may capture an earlier stage of dysglycaemia.