USMLE Step 1 Question 354

Question:

A 50-year-old male with a history of diabetes returns to his physician’s office for review of his labs. His health maintenance labs show a hemoglobin A1c of 9.0, increased from 7.0 at his last visit. His current drug regimen includes glipizide and metformin. He reports that he takes his medications regularly, but his wife is concerned about his diabetes control. Which of the following labs would best indicate a need for insulin to control this patient’s blood sugar?

Correct Answer: B.  C-peptide

Insulin-resistant diabetes, aka adult-onset or Type II, eventually becomes insulin dependent when overworked pancreatic beta cells stop producing insulin. One way to determine when insulin therapy is indicated is to check a C-peptide (Answer B). C-peptide is cleaved when pro-insulin is converted to insulin; normal ranges of C-peptide indicate endogenous production of insulin.

Choice A is incorrect. Anti-GAD antibody is used to diagnose Type I, or autoimmune Diabetes.

Choices C and E are incorrect. A random blood glucose >200 or a fasting blood glucose >126 is used to diagnose Diabetes. Measurement of blood glucose is not a reliable test of insulin production.

Choice D is incorrect. IGF-1 level is used to diagnose growth hormone abnormalities.