INS and diabetes mellitus: Measurement of fasting, random, or stimulated C-peptide concentrations, as an indicator of pancreatic beta-cell insulin secretion, is recommended in patients with new-onset diabetes to identify specific diabetes subtypes (type 1 and type 2 diabetes and maturity-onset diabetes of the young), patients that require timely insulin replacement therapy, and also to predict response to oral hypoglycaemic agents (1, 2).