C-peptide is measured to tell the difference between insulin the body produces and insulin that is injected into the body.

Someone with type 1 or type 2 diabetes may have their C-peptide level measured to see if their body is still producing insulin. C-peptide is also measured in case of low blood sugar to see if the person’s body is producing too much insulin.

The test is also often ordered to check certain medicines that can help the body produce more insulin, such as glucagon-like peptide 1 analogs (GLP-1) or DPP IV inhibitors.