Assessing C-peptide levels in blood is a reliable method of determining insulin production. The pancreas secretes insulin, which enters the bloodstream and facilitates the uptake of sugar by cells for energy production. Insulin thus controls blood sugar levels. The C-peptide test aids in managing diabetes therapy, determining the kind of diabetes you have, and determining the reason behind low blood sugar levels. A high level of C-peptide indicates excessive insulin production in the body, which is indicative of Type 2 diabetes and Cushing syndrome. Low C-peptide levels are indicative of inadequate insulin production, which can be seen in Addison’s disease and Type 1 diabetes. Diabetes is not diagnosed using this test.