title: Pseudoinsulinoma in a white man with autoimmune hypoglycemia due to anti-insulin antibodies: value of the free C-Peptide assay.
abstract: OBJECTIVE
  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.
authors.affiliation: From the Division of Endocrinology, Diabetes, & Metabolism and.
authors.forename: Audrey E
authors.initials: AE
authors.lastname: Arzamendi
authors.affiliation: Laboratory for Atherosclerosis & Metabolic Research, Departments of Pathology and Internal Medicine, UC Davis Medical Center, Sacramento, CA; and.
authors.forename: Uthra
authors.initials: U
authors.lastname: Rajamani
authors.affiliation: From the Division of Endocrinology, Diabetes, & Metabolism and Laboratory for Atherosclerosis & Metabolic Research, Departments of Pathology and Internal Medicine, UC Davis Medical Center, Sacramento, CA; and Veterans Affairs Medical Center, Mather, CA. ijialal@ucdavis.edu.
authors.forename: Ishwarlal
authors.initials: I
authors.lastname: Jialal
mesh_terms: D001323:Autoantibodies / Q000378:metabolism; D001327:Autoimmune Diseases / Q000175:diagnosis / Q000276:immunology*; D002096:C-Peptide / Q000032:analysis* / Q000276:immunology; D006801:Humans; D007003:Hypoglycemia / Q000175:diagnosis / Q000209:etiology* / Q000378:metabolism*; D007328:Insulin / Q000276:immunology; D007330:Insulin Antibodies / Q000276:immunology*; D008297:Male; D008875:Middle Aged
chemical_list: D001323:Autoantibodies; D002096:C-Peptide; D007328:Insulin; D007330:Insulin Antibodies
keywords: Anti-insulin antibodies; Autoimmune hypoglycemia syndrome; Free C-peptide assay; Hirata disease; Insulin autoimmune syndrome