To enable early, preclinical diagnosis of T1D, its progression is described in three stages:

Stage 1: normoglycemia with at least two positive autoantibodies.

Stage 2: dysglycemia with autoantibodies.

Stage 3: clinical diabetes when beta cells decline to 20–30%.

The importance of genetic risk scores, autoantibodies, and metabolic markers is highlighted for assessing individual risk. The need to consider the clinical, immunological, and genetic diversity of T1D is emphasized to better classify patients.

Therapeutic advances, notably the approval of teplizumab, which delays progression from stage 2 to stage 3 by two to three years, are presented. This demonstrates that early diagnosis and precision medicine enable the development of effective secondary prevention strategies.