Which statement about C-peptide in distinguishing diabetes types is true?

• A. It measures insulin in the bloodstream directly.
• B. It is produced by the liver.
• C. It indicates insulin resistance by measuring receptor activity.
• D. C-peptide reflects endogenous insulin production; low in Type 1; normal to high in early Type 2.

Answer: (D)

C-peptide reflect endogenous insulin production; low in Type 1; normal to high in early Type 2.

C-peptide is produced when the pancreas releases insulin, as proinsulin is split into insulin and C-peptide in beta cells. Because C-peptide and insulin are released in equal amounts, measuring C-peptide gives a reliable readout of how much insulin the body is producing. Unlike insulin, C-peptide isn’t cleared by the liver quickly and has a longer, more stable presence in the blood, making it a good marker of endogenous insulin secretion. In Type 1 diabetes, autoimmune destruction of beta cells leads to little or no insulin production, so C-peptide levels are low. In the early stages of Type 2 diabetes, the body often makes more insulin to overcome insulin resistance, so C-peptide levels tend to be normal or high. This contrast helps clinicians distinguish between the two types, especially when patients are on insulin therapy, where direct insulin measurements could be misleading.