C-peptide (C-peptide) and insulin (insulin) are two molecules produced by pancreatic islet cells during insulin synthesis. Source difference: C-peptide is a by-product of insulin synthesis by islet cells. When insulin is synthesized, C-peptide is synthesized at the same time. Therefore, C-peptide can only be synthesized in the islet cells and will not be produced by cells outside the islets. Insulin is the main hormone synthesized by pancreatic islet cells and released into the blood, which controls blood sugar levels and promotes the absorption and utilization of glucose. Function difference: The main function of C-peptide is to maintain the balance between insulin and insulin receptors, and to participate in the synthesis and secretion of insulin.  The level of C-peptide can indirectly reflect the functional state of islet cells and is used as an index to evaluate the function of islets. Insulin is the main metabolic hormone, which promotes the uptake and utilization of glucose by cells, lowers blood sugar concentration, and regulates the metabolic process of fat and protein. Blood concentration difference: C-peptide blood levels are more stable than insulin levels because it is cleared more slowly. The blood concentration of insulin is affected by many factors, including food intake in the gastrointestinal tract, islet cell function, insulin resistance, etc.In summary, C-peptide is a by-product of insulin used primarily to assess islet cell function, whereas insulin is the major metabolic hormone used to regulate blood