C-Peptide
C-peptide is a fragment released in equal amounts to insulin when your pancreas makes insulin. Measuring it gives an indirect but reliable estimate of how much insulin your own body is producing.
Because C-peptide comes only from insulin your body makes (not from injected insulin), it helps clinicians gauge how well your pancreas is working. It can help distinguish between different types of diabetes and clarify whether the body is still producing meaningful amounts of insulin. This makes it a useful complement to glucose and insulin testing.
A higher C-peptide suggests your pancreas is producing a lot of insulin, which can accompany insulin resistance. Kidney function influences C-peptide levels as well, since the kidneys clear it. Your clinician interprets the value alongside your glucose and clinical history.
A lower C-peptide suggests your pancreas is making less insulin, which is meaningful in the context of your blood sugar. It is always read together with a matching glucose level.
There is no single ideal C-peptide number, since it depends on your glucose at the time and the reason for testing. Your clinician will explain what your result means for your situation.
Sources
Educational context only, not medical advice or a diagnosis. Reference ranges vary by lab, age and sex; always discuss your results with a clinician.