This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Pathology
After suffering a seizure, a 23-year old woman is found to have profound hypoglycemia. Determination of which of the following would aid in differentiating exogenous hyperinsulinemia from endogenous hyperinsulinemia? 
Select and explain. 
A. C-peptide, B. Gastrin, C. Glucagon, D. Proinsulin
A: C-peptide
Answer: A: C-peptide 
Explanation: - Distinguishing endogenous insulin production from exogenous insulin (therapeutically or surreptitiously administered) is done by quantitation of C-peptide. - C-peptide Fragment of proinsulin molecule which split off during synthesis of insulin. Circulating C-peptide is characteristically increased in patients with increased endogenous insulin production. C peptide is not increased in exogenous insulin administration, because it is removed during purification of commercial insulin preparations.