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C-peptide during the prolonged fast in insulinoma
F J Service1, P C O'Brien, M M McMahon
1Division of Endocrinology and Metabolism, Mayo Clinic, Rochester, Minnesota 55905.
The Journal of Clinical Endocrinology and Metabolism
|March 1, 1993
Summary
This study establishes diagnostic criteria for insulinoma using a prolonged fasting test. Elevated C-peptide levels during fasting confirm insulinoma in patients negative for sulfonylurea.
Area of Science:
- Endocrinology
- Clinical Diagnostics
- Biochemistry
Background:
- Insulinoma diagnosis relies on identifying endogenous hyperinsulinism.
- Established diagnostic criteria for insulinoma using C-peptide during prolonged fasting are lacking.
Purpose of the Study:
- To establish diagnostic criteria for insulinoma using C-peptide levels during a prolonged fasting test.
- To differentiate insulinoma from factitious hypoglycemia.
Main Methods:
- A prolonged fasting protocol (up to 72 hours) was administered to patients with confirmed insulinoma, normal subjects, and patients with factitious hypoglycemia.
- Plasma glucose, C-peptide, and insulin levels were measured serially.
- Plasma was tested for sulfonylurea to exclude exogenous insulin administration.
Main Results:
- Insulinoma patients exhibited significantly higher C-peptide levels (≥ 0.20 nmol) at the end of fasting compared to normal subjects (≤ 0.10 nmol) when plasma glucose was ≤ 2.8 mmol.
- All patients tested were negative for sulfonylurea.
- Whipple's triad was observed in insulinoma patients during the fast.
Conclusions:
- A C-peptide concentration ≥ 0.20 nmol during a prolonged fast, in conjunction with Whipple's triad and a negative sulfonylurea test, confirms insulinoma.
- This protocol provides reliable diagnostic criteria for insulinoma.