How is a biochemical diagnosis of insulinoma established?

Updated: May 31, 2020
  • Author: Zonera Ashraf Ali, MBBS; Chief Editor: Neetu Radhakrishnan, MD  more...
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The biochemical diagnosis of insulinoma is established in 95% of patients during prolonged fasting (up to 72 h) when the following results are found:

  • Serum insulin levels of 10 µU/mL or more (normal < 6 µU/mL)

  • Glucose levels of less than 40 mg/dL

  • C-peptide levels exceeding 2.5 ng/mL (normal < 2 ng/mL)

  • Proinsulin levels greater than 25% (or up to 90%) of immunoreactive insulin levels

  • Screening for sulfonylurea negative

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