INS and diabetes mellitus: Prior research in adults has shown that a glucagon-stimulated C-peptide level of 0.9–1.8 ng/mL could be used to differentiate insulin-requiring from non-insulin-requiring diabetes, and patients with a glucagon-stimulated C-peptide level < 0.2 nmol/L (0.6 ng/mL) might be likely to have an absolute requirement for insulin [10,11].