C Peptide test is a simple blood test to measure insulin secretion produced by the pancreas. This test gives clarity between insulin secreted by the body and insulin injected into the body in Diabetic patients. C-peptide has a half-life of 30 minutes and tends to stay in the body longer than insulin. Insulin has a half-life of 15 mins. Therefore, this test is an excellent way to measure insulin levels, especially insulin levels produced by the pancreas and exclude the insulin level in the bloodstream from injected insulin.