Defining the Decline in Endogenous Insulin Secretion in Type 1 Diabetes Diagnosed After 30 Years of Age.

The study aims to evaluate progression of type 1 diabetes. Primary analysis will be conducted on those with \>=1 diabetes autoantibody positive (GAD, IA2 ZNT8). Sensitivity analysis will be performed by repeating all analysis defining T1D as a) double antibody positivity and b) single antibody positivity combined with a high genetic risk score for T1D (T1DGRS\>5th centile of a control population). Further aims will be to evaluate the utility of dried blood spot testing to detect change in C-peptide and the utility of home test results as a marker of hypoglycaemia and glucose variability.