CGM-derived index correlates with beta cell function and subsequent glycaemia in islet autoimmunity

Researchers evaluated a continuous glucose monitoring (CGM)-derived disposition index as a proxy for beta cell function in people with at least one islet autoantibody who did not require insulin treatment. The observational study enrolled 24 participants, with a median age of 16.8 years. Participants underwent a three-hour, 10-point OGTT while wearing blinded CGM. The CGM-derived index used sensor data during the glucose load and two blood glucose calibrations and was compared with an oral minimal-model index derived from glucose, insulin and C-peptide measurements.

Eighteen participants completed baseline testing and repeat CGM one year later: ten had pre-stage 1 disease, seven stage 1 and one stage 3a. The baseline CGM-derived index correlated strongly with the reference index (r=0.90; p<0.001). Lower baseline values were associated with more time above 7.8 mmol/l (140 mg/dl) at one year (r=−0.61; p=0.014) and higher mean sensor glucose (r=−0.62; p=0.020).

The findings suggest a potential approach to estimating beta cell function with fewer blood measurements than conventional OGTT-based modelling. However, the method still required a glucose load and blood glucose calibrations, rather than routine free-living CGM alone. The small cohort, limited disease-stage representation and reliance on glycaemic surrogate outcomes limit clinical interpretation; these correlations do not establish prediction of progression to insulin-requiring diabetes.