Stimulated C-Peptide Test

The C‑peptide stimulation test measures endogenous insulin production by assessing C‑peptide levels before and after a stimulus (commonly IV glucagon or a mixed meal). It evaluates pancreatic beta‑cell reserve: a rise indicates residual insulin secretion, while little or no increase suggests beta‑cell failure (as in type 1 diabetes) or exogenous insulin use. It helps distinguish causes of hypoglycemia and guide treatment.

A normal stimulated C‑peptide (measured after a mixed meal or glucagon) is generally >1.8 ng/mL (≈0.6 nmol/L), indicating preserved beta‑cell function. Values of ~0.6–1.8 ng/mL may be borderline, while a stimulated C‑peptide below ~0.6 ng/mL (≈0.2 nmol/L) usually reflects severe insulin deficiency. Exact cutoffs can vary by lab and testing method.

High C‑peptide indicates increased endogenous insulin production. Causes include insulin resistance (obesity, metabolic syndrome, type 2 diabetes), insulinoma, or recent sulfonylurea use. It helps distinguish endogenous from injected insulin. Persistently high levels signal worsening insulin resistance and higher cardiovascular/metabolic risk; evaluation should identify underlying cause and optimize glycemic control and risk factors.

To stimulate C‑peptide (a marker of endogenous insulin), preserve and activate pancreatic beta cells: optimize blood glucose, lose weight, exercise, and use a mixed‑meal or glucose challenge to provoke release. Medications that boost insulin secretion—sulfonylureas, meglitinides, GLP‑1 receptor agonists or DPP‑4 inhibitors—can raise C‑peptide if residual function exists. For severe failure, islet/pancreas transplant may be considered; consult your clinician.

The cost of a C‑peptide blood test varies by country and provider. In India it’s commonly around ₹300–₹1,200. In the UK it’s usually provided free on the NHS, while private testing costs about £20–£80. In the US out‑of‑pocket prices typically range from roughly $30 to $200, depending on the lab and insurance coverage.

Yes — many people with type 2 diabetes can achieve remission, especially when diagnosed early. Significant sustained weight loss (often 10–15% body weight), low‑calorie or very low‑calorie diets, increased physical activity, and bariatric surgery can normalize blood glucose and allow stopping medications under medical supervision. Remission isn’t guaranteed; ongoing lifestyle maintenance and monitoring are required because diabetes can return.