CGM-derived disposition index estimates beta cell function in individuals with islet autoimmunity who do not require...

Monitoring of beta cell function in individuals with islet autoimmunity who do not require insulin treatment (preclinical type 1 diabetes) is normally done via OGTTs, posing major challenges given the invasiveness of the test. Here, we validated a disposition index (DI) derived from continuous glucose monitoring (CGM) metrics (DI^CGM), which is a proxy of beta cell function, against the gold-standard OGTT DI (DI^MM), in a cohort of individuals with one or more islet autoantibodies who do not require insulin treatment.

Participants underwent a 3 h 10-point OGTT with measurement of glucose, insulin and C-peptide while wearing a blinded CGM. The sensor was started 24 h prior to the OGTT. DI^CGM was computed using CGM data during the 3 h OGTT and two blood glucose calibrations, and compared with the DI from the oral minimal model (DI^MM), which uses plasma glucose, insulin and C-peptide. The association between the baseline DI^CGM and duration of glucose levels above 7.8 mmol/l (140 mg/dl) (TA140) at 1 year was explored.

Twenty-four participants (median age 16.8 years [IQR 13.5-27.7] ) were enrolled, of whom 18 completed both the OGTT (ten with pre-stage 1, seven with stage 1 and one with stage 3a type 1 diabetes) and CGM at baseline, and had repeat CGM 1 year later. The baseline DI^CGM was highly correlated with the DI^MM (r=0.90, p<0.001). Lower baseline DI^CGM was associated with higher 1 year TA140 (r=-0.61, p=0.014) and higher 1 year mean sensor glucose (r=-0.62, p=0.020).

Beta cell function can be estimated using CGM during a glucose load. DI^CGM correlates with a 1 year clinically relevant outcome (TA140) in individuals with islet autoimmunity who do not require insulin therapy.