July 24, 2012

Concerning hormones

A 17 year old patient has had two episodes of severe hypoglycemia. He is being investigated for a possible insulinoma but is also suspected of factitious (self-medication) insulin-induced hypoglycemia by injection of insulin. His plasma insulin levels are elevated.

Which of the following is most likely to help in confirming self-induced hypoglycemia?

a) weekly early morning plasma insulin levels
b) hemoglobin level
c) serum glucose level
d) plasma C-peptide hormone level
e) a weekly weight chart






ANSWER
The correct answer is D


Explanation
Among the causes of recurrent hypoglycemic episodes in seemingly healthy patients, discriminating between sulfonylurea-induced hypoglycemia and insulinoma is of utmost importance because of the indistinguishable biochemical constellation. Inappropriately elevated serum levels of insulin and C-peptide during hypoglycemia are characteristic features of both conditions.

In contrast, hypoglycemia caused by exogenous insulin administration is associated with a high serum insulin level and a low serum C-peptide. Molar ratio of insulin to C-peptide in a hypoglycemic patient in excess of 1.0 is indicative of exogenous insulin administration. A ratio less than 1.0 is found in both insulinoma and sulfonylurea intake.1 Determination of insulin antibodies to prove exogenous insulin administration is not recommended because of the high degree of purity of current insulin preparations and the lack of specificity.2

References
  1. Lebowitz MR, Blumenthal SA: The molar ratio of insulin to C-peptide: an aid to the diagnosis of hypoglycemia due to surreptitious (or inadvertent) insulin administration. Arch Intern Med 153:650-55, 1993.
  2. Service FJ: Hypoglycemic disorders. N Engl J Med 332:1144-52, 1995.
Source(s): Wiesli P, Lehmann R: Pitfalls in the Evaluation of Spontaneous Hyperinsulinemic Hypoglycemia. Diabetes Spectrum. Volume 13 Number , 2000, Page 56. Available online: http://journal.diabetes.org/diabetesspectrum/00v13n1/pg56.htm

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