Pseudoinsulinoma in a white man with autoimmune hypoglycemia due to anti-insulin antibodies: value of the free C-Peptide assay

Audrey E. Arzamendi, Uthra Rajamani, Ishwarlal Jialal

Research output: Contribution to journalArticle

9 Scopus citations


OBJECTIVES: Insulin autoimmune syndrome (IAS) is an extremely rare cause of hypoglycemia, particularly in non-Asian populations.

METHODS: In this report, we describe a white male patient with elevated total insulin (>100.0 μIU/mL), C-peptide, and proinsulin levels who was diagnosed with IAS due to anti-insulin antibodies. He also had a small IgG κ M-protein.

RESULTS: We show that anti-insulin antibodies and/or the monoclonal protein can significantly interfere with insulin and C-peptide immunoassays and propose polyethylene glycol precipitation to quantitate free C-peptide levels as a useful assay in differentiating IAS due to anti-insulin antibodies from insulinoma.

CONCLUSIONS: In patients presenting with hypoglycemia with excessively high insulin levels, consideration needs to be given to autoimmune hypoglycemia due to anti-insulin antibodies as a cause. Additionally, if total C-peptide levels are increased, free C-peptide needs to be quantitated following polyethylene glycol precipitation.

Original languageEnglish (US)
Pages (from-to)689-693
Number of pages5
JournalAmerican Journal of Clinical Pathology
Issue number5
StatePublished - Nov 1 2014



  • Anti-insulin antibodies
  • Autoimmune hypoglycemia syndrome
  • Free C-peptide assay
  • Hirata disease
  • Insulin autoimmune syndrome

ASJC Scopus subject areas

  • Medicine(all)

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