A 21-year-old nurse is found to have fasting hypoglycemia with elevated insulin levels. All of the following would be appropriate steps in her further evaluation except:
A. Measure insulin antibodies.B. Measure C-peptide levels.
C. Perform a CT scan of the pancreas.
D. Measure plasma or urine sulfonylurea levels.
E. None of the above
Answer. C. Perform a CT scan of the pancreas.
Elevated insulin levels in association with
hypoglycemia are indicative of an insulinoma, surreptitious insulin,
sulfonylurea agents, or circulating insulin antibodies. In surreptitious
insulin administration, insulin levels would be elevated and C-peptide levels
would be low because exogenous insulin administration suppresses ,B-cell
production of insulin. In an insulin-producing tumor or ingestion of a
sulfonylurea, both insulin and C peptide would be elevated. Insulin antibodies
can cause hypoglycemia by binding and then releasing insulin. Insulin
antibodies can interfere with the radioimmunoassay and can result in
artifactual high insulin values. Insulin antibodies can be a clue to
surreptitious insulin administration in a nondiabetic patient. It takes several
months for insulin antibodies to develop. High C-peptide levels essentially
rule out an exogenous source of insulin. Sulfonylureas can cause elevated
insulin levels and elevated C-peptide levels. Ingestion of sulfonylureas can be
ruled out by measuring plasma or urine levels of sulfonylureas. A CT scan of
the pancreas is of little value because most insulinomas are extremely small
and cannot be seen on CT scan. 