Glycation gap size, stability over time and correlates in people with Type 1 diabetes

Uptake of Continuous Glucose Monitoring (CGM) by people with Type 1 diabetes is increasing. As well as real-time glucose metrics, CGM can estimate a HbA1c level from 2-weeks to 3-months of CGM data. Differences between laboratory-based and CGM-estimated HbA1c values, termed the glycation gap, can occur. Little knowledge exists about the glycation gap stability over time and of the correlates and determinants of the glycation gap. In our Australian tertiary-referral diabetes clinic we conducted a cross-sectional study of the glycation gap in 316 adults and a longitudinal study in 231 of these participants. We found frequent differences between laboratory and CGM-estimated HbA1c measures, with 64% of 316 adults having a glycation gap ≥0.3%. Whilst the glycation gap was stable over time in groups, in 118/231 adults (51%) it changed by ≥0.3%. We also evaluated correlates of the glycation gap. The glycation gap correlated inversely with age, HbA1c and haematocrit and correlated positively with eGFR and mean corpuscular haemoglobin concentration. The glycation gap differed between CGM brands, but not by insulin delivery modality. Further studies are merited to explore factors associated with larger and changing glycation gaps, as they are relevant to clinical practice.