The test is called as fasting C Peptide levels. But do not get it done yourself. It requires certain adjustments in your medicines before testing. Also its interpretation requires the doctor to know your diabetes history

Hello, Are you asking about type 1 diabetes ??where insulin secretion by pancrease is decreased.... It’s rare. Only about 5% of people with diabeteshave type 1. If doctor thinks of type 1 diabetes, he’ll check blood sugar levels. He may test urine for glucose or chemicals body makes when one don’t have enough insulin. It's juvenile starts at early age . life long insulin injection is recommended.