INS and type 1 diabetes mellitus: The Joslin 50-year medalist study found that most of the T1DM participants with a duration of 50 years or more reached endogenous clinical insulin secretion (random C − peptide ≥ 0.03 pmol/mL) [4], and 2.6% had random serum C − peptide ≥ 0.20 pmol/mL.