Low or absent C-peptide is most consistent with which type of diabetes?

• A. Type 1 diabetes
• B. Type 2 diabetes
• C. Gestational diabetes
• D. Prediabetes

Answer: (A)

C-peptide levels reflect how much insulin the pancreas is producing on its own, since C-peptide is released in equal amounts with insulin when beta cells secrete insulin.

In type 1 diabetes, autoimmune destruction of beta cells severely reduces or eliminates endogenous insulin production, so C-peptide becomes very low or absent. This is the hallmark that helps distinguish it from other forms where some insulin is still made.

In type 2 diabetes, insulin production is typically preserved or even increased early on, so C-peptide levels are normal or elevated rather than low. Gestational diabetes involves insulin resistance during pregnancy with relatively preserved or compensatorily increased insulin secretion, so C-peptide tends to be normal or high. Prediabetes also features impaired glucose tolerance with ongoing or compensatory insulin production, so C-peptide is not low.

Thus, low or absent C-peptide most strongly points to type 1 diabetes.