Fasting c-peptide 1.72ng/ml is between the normal value of 0.78 and 1.89ng/ml, which is normal, and is generally used to detect whether the function of pancreatic β-cells is normal or not, and to assist in the diagnosis of the type of diabetes mellitus. However, due to the different examination methods and reagents, the reference indexes of each hospital are different and need to be analyzed specifically. c-peptide is a peptide cleaved during the production of insulin. 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 partially excreted from the urine in its original form. Blood C-peptide concentration is not interfered by exogenous insulin and anti-insulin antibodies, and can more accurately reflect the function of pancreatic β-cells. Since C-peptide is not affected by insulin injection, changes in C-peptide better reflect the function of pancreatic β-cells in patients receiving insulin therapy to guide patients in adjusting the dosage of insulin or deciding whether to continue treatment. When the body’s fasting c-peptide value is abnormal, the cause should be clarified under the guidance of the doctor, the diagnosis of diabetes mellitus should be confirmed, and active treatment should be carried out.