There are two practices of C-peptide test: first, for the first diagnosis of diabetes mellitus patients for islet function examination, you can drink the standard 75g glucose for C-peptide release test examination, fasting blood for C-peptide measurement, drink sugar water and then draw blood again 1 hour, 2 hours and then draw blood again, and through the results of the pancreatic islet function to judge. Secondly, for hospitalized patients with diagnosed diabetes to review islet function, generally a simplified clinical program will be used, which is to eat two steamed buns in the morning for the corresponding C-peptide release test, C-peptide release test and insulin release test is different in that the C-peptide release test is not subjected to exogenous insulin, that is to say, if oral sulfonylureas or insulin can not be done to do the insulin release test, only the C-peptide release test can be done to the C-peptide release test. The C-peptide release test is used to determine the function of the pancreatic islets.