How is a biochemical diagnosis of insulinoma made?

Updated: May 31, 2020
  • Author: Zonera Ashraf Ali, MBBS; Chief Editor: Neetu Radhakrishnan, MD  more...
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The biochemical diagnosis is established in 95% of patients during prolonged fasting when the following parameters are found:

  • Serum insulin levels of 10 µU/mL or more (normal
  • Glucose levels of less than 40 mg/dL
  • C-peptide levels exceeding 2.5 ng/mL (normal
  • Proinsulin levels ≥22 pmol/L, [27] or greater than 25% (or up to 90%) that of immunoreactive insulin
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    Stimulation tests are no longer recommended. The intravenous administration of tolbutamide, glucagon, or calcium can be hazardous, as it may induce prolonged and refractory hypoglycemia.

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