Question on C-peptide

 A 32 year-old female comes regularly to your office with symptoms of hypoglycemia. After a few visits, you’ve become suspicious of possible factitious insulin self-injections. Which of the following tests is most useful to detect factitious insulin injections? 

A.Serum insulin level 

B.C-peptide level 

C.serum glucose level 

D.serum albumin level 

E.serum bilirubin level 

Correct Answer is B. C-peptide is an inactive by-product of the cleavage of proinsulin to active insulin. It is produced in equal amounts to insulin. Its presence indicates endogenous release of insulin and its absence indicates exogenous insulin administration. Serum insulin, glucose, albumin and bilirubin level will not help to detect exogenous insulin administration. 

Q.In which of the following conditions, is the level of C-peptide increased in blood? 

A.Sulfonylurea ingestion 

B.Type 1 diabetes mellitus 

C.Therapeutic insulin administration 

D.Factitious insulin administration 

E.All the above 

Correct Answer is A. C-peptide level is increased in sulfonylurea ingestion and insulinoma and is decreased in Type 1 diabetes mellitus (decreased endogenous insulin), and insulin administration (therapeutic or factitious). 

References: 

Guide to Diagnostic Tests, 7e

Gomella and Haist’s Clinician’s Pocket Reference, 12e

Leonard G. Gomella, Steven A. Haist