High C-peptide normal blood glucose may be caused by conditions such as Cushing’s syndrome, pheochromocytoma, etc. It is advisable to consult your doctor. C-peptide is a peptide cleaved during insulin production. It has a longer half-life than insulin (about 35 minutes), is not inactivated by hepatic enzymes, and is only degraded in the kidneys, and partly excreted from the urine in its original form. Blood C-peptide concentrations are not interfered with by exogenous insulin or anti-insulin antibodies, and reflect more accurately the function of pancreatic β-cells. Pheochromocytoma, a tumor that originates from chromophobe tissue and secretes catecholamines, may present with metabolic disorders and subsequent elevation of blood glucose, but the C-peptide is normal because the function of pancreatic islet β-cells is not disrupted. Cushing’s syndrome, which is caused by excessive secretion of glucocorticoids, may also present with elevated blood glucose but normal C-peptide. If C-peptide is normal but blood glucose is elevated, it is recommended to go to the hospital and ask the doctor to make a judgment.