Postprandial C‑peptide is the C‑peptide level measured after a meal, typically 1–2 hours postprandial or during a mixed‑meal tolerance test, reflecting endogenous insulin secretion in response to food. Because C‑peptide is released equimolarly with insulin and not heavily cleared by the liver, postprandial values assess residual beta‑cell function, help classify diabetes, and distinguish endogenous from injected insulin.

Yes — a fasting C‑peptide (after an 8–10 hour fast) is usually preferred to provide a baseline measure of endogenous insulin production. For more sensitive assessment of beta‑cell reserve, clinicians may use stimulated tests (mixed‑meal or glucagon). Some insulin‑secretagogue medications may need withholding per clinician advice. Follow your laboratory’s instructions before testing.

Type 2 diabetes is usually associated with normal or elevated C‑peptide, reflecting preserved or increased insulin production. Fasting C‑peptide above about 1.0 ng/mL — and particularly levels >2.0 ng/mL — or stimulated values above the usual reference range (~0.5–2.0 ng/mL) suggest insulin resistance and type 2 diabetes. Very low or undetectable C‑peptide indicates insulin deficiency/type 1 diabetes.

C-peptide is not a general tumor marker. It’s a peptide released with endogenous insulin and is used to assess pancreatic beta-cell function and to distinguish endogenous insulin production (for example, insulinoma) from exogenous insulin administration. Elevated C‑peptide can suggest an insulin-secreting tumor, but it’s primarily a metabolic/endocrine diagnostic tool rather than a broad cancer marker.

A normal C‑peptide after eating is typically higher than fasting—commonly about 1.5–4.0 ng/mL (≈0.5–1.3 nmol/L), though exact ranges vary by lab and timing. Values below ~0.6 ng/mL suggest very low insulin production; markedly higher levels may indicate insulin resistance. Always interpret results using your laboratory’s reference range and discuss abnormal findings with your clinician.

Type 2 diabetes can often be put into remission but not reliably "cured." Significant, sustained weight loss—achieved through low‑calorie diets, increased physical activity, or bariatric surgery—can normalize blood glucose and allow stopping medications, especially when diagnosed early. Remission depends on remaining beta‑cell function; ongoing monitoring and weight maintenance are essential because blood sugar often returns if weight is regained.