Below are images of my C-Peptide blood test results. C-peptide is what your pancreas produces when it produces insulin, kind of like a byproduct of insulin production.  A healthy non diabetic should have a fasting level of >1.0 ng/mL. Long term type 1 diabetics will likely have a fasting C-peptide level of 0 ng/mL, since they no longer produce insulin. The tests below show that my C-peptide levels have gradually increased, with my highest result so far coming in at 0.80 ng/mL.