C-peptide (Serum or Plasma) Concentration

Why This Test Is Done

Doctors may order a C-peptide test to check if your pancreas is making insulin on its own, especially in people with diabetes or suspected insulin dependency. It can also help diagnose conditions like insulinoma (a rare tumor that causes excessive insulin production) or monitor how well diabetes treatments are working.

How the Test Works

A small blood sample is taken from a vein in your arm. The sample is sent to a lab where it’s analyzed to measure C-peptide levels. This test doesn’t require fasting unless directed by your healthcare provider.

What to Expect Before the Test

No special preparation is needed, but inform your doctor about any medications you’re taking, especially insulin or diabetes drugs, as they may affect results. Avoid alcohol before testing if advised.

Possible Results and Interpretation

Results are compared to a reference range, but exact values can vary by lab. High levels may suggest overproduction of insulin (e.g., insulinoma), while low levels could indicate insufficient natural insulin production (e.g., diabetes). Your doctor will interpret results in the context of your overall health.