C-peptide is an isomolecular peptide that is split from insulinogen at the same time as insulin, and plasma insulin should rise to a peak at 30-60 minutes after eating, with a peak of 5-10 times the basal level, and should return to the basal level 3-4 hours after eating. It should return to basal level 3-4 hours after feeding. However, many diabetic patients have been treated with insulin before admission to hospital, or have been treated with insulin intravenously for hyperglycemia during hospitalization because of severe hyperglycemia, and this part of insulin will affect the measurement of plasma insulin, but C-peptide, which splits in parallel with insulin, is not affected by the above, and normally peaks at 30-60 minutes after feeding, with a peak value of 5-6 times the basal value.