C peptide mainly refers to fasting C peptide, the normal value is 0.3~1.3nmol/L, the results vary from machine to machine, it is recommended to consult your local doctor. C peptide is a peptide, fasting C peptide is similar to serum insulin, which can be used for the diagnosis of diabetes mellitus typing, but also can evaluate the pancreatic β-cell secretion function and reserve function, and even can guide the insulin dosage. If the level of C-peptide increases, it often suggests pancreatic islet β-cell tumor, liver cirrhosis, etc., and the level decreases suggests diabetes. In clinical practice, in addition to C-peptide level, C-peptide release test, insulin, C-peptide/insulin ratio and other indicators are also used to diagnose diseases. Abnormal C-peptide indicators are recommended for timely diagnosis and treatment.