title: Diagnosis of insulin autoimmune syndrome using polyethylene glycol precipitation and gel filtration chromatography with ex vivo insulin exchange.
abstract: BACKGROUND
  Insulin-binding antibodies may produce severe dysglycaemia in insulin-naïve patients ('insulin autoimmune syndrome' (IAS) or Hirata disease), while rendering routine insulin assays unreliable.
  
  
  OBJECTIVE
  To assess the performance of clinically used insulin assays and an optimal analytical approach in the context of IAS.
  
  
  METHODS
  Observational biochemical study of selected patients with hyperinsulinaemic hypoglycaemia.
  
  
  METHODS
  Three patients without diabetes with recurrent spontaneous hyperinsulinaemic hypoglycaemia and 'positive' insulin antibodies.
  
  
  METHODS
  A panel of clinically used insulin assays (Siemens ADVIA®Centaur, Siemens Immulite®2000, DiaSorin LIAISON®XL, PE AutoDELFIA®and the Beckman Coulter Access®2) were used before and after plasma dilution or polyethylene glycol (PEG) precipitation. Anti-insulin IgG antibodies were measured by Isletest™-IAA ELISA. Gel filtration chromatography (GFC) was undertaken with and without preincubation of plasma with exogenous insulin.
  
  
  RESULTS
  Dilution of IAS plasma with assay-specific buffer increased insulin recovery, supporting negative immunoassay interference by antibodies. PEG precipitation of IAS plasma decreased insulin recovery using all assays except the Immulite®2000. GFC discriminated high molecular weight and monomeric insulin, while ex vivo addition of exogenous insulin to plasma increased insulin bound to antibody, thereby improving the sensitivity of detection of insulin immunocomplexes.
  
  
  CONCLUSIONS
  Immunoprecipitation with PEG must be used with caution in screening for insulin-antibody complexes as results are assay dependent. GFC with addition of exogenous insulin can identify significant insulin immunocomplexes with enhanced sensitivity, with attendant greater clinical utility and avoidance of radiolabelled reagents.
authors: The University of Cambridge Metabolic Research Laboratories, Wellcome Trust-MRC Institute of Metabolic Science, Cambridge, UK.|The National Institute for Health Research Cambridge Biomedical Research Centre, Cambridge, UK.|The Pathology Partnership, Department of Clinical Biochemistry and Immunology, Addenbrooke's Hospital, Cambridge, UK.
authors: David
authors: D
authors: Church
authors: Department of Endocrinology, Diabetes and Metabolism, Centro Hospitalar e Universitário de Coimbra, Coimbra, Portugal.
authors: Luís
authors: L
authors: Cardoso
authors: The Pathology Partnership, Department of Clinical Biochemistry and Immunology, Addenbrooke's Hospital, Cambridge, UK.
authors: Sonia
authors: S
authors: Bradbury
authors: Department of Clinical Biochemistry, Western General Hospital, NHS Lothian, Edinburgh, UK.
authors: Catriona
authors: C
authors: Clarke
authors: Cambridge University Hospitals NHS Foundation Trust, Cambridge Biomedical Campus, Cambridge, UK.
authors: Anna
authors: A
authors: Stears
authors: Edinburgh Centre for Endocrinology and Diabetes, Royal Infirmary of Edinburgh, Edinburgh, UK.
authors: Anna
authors: A
authors: Dover
authors: The Pathology Partnership, Department of Clinical Biochemistry and Immunology, Addenbrooke's Hospital, Cambridge, UK.
authors: David
authors: D
authors: Halsall
authors: The University of Cambridge Metabolic Research Laboratories, Wellcome Trust-MRC Institute of Metabolic Science, Cambridge, UK.|The National Institute for Health Research Cambridge Biomedical Research Centre, Cambridge, UK.
authors: Robert
authors: R
authors: Semple
mesh_terms: D000328:Adult; D001327:Autoimmune Diseases / Q000175:diagnosis*; D011232:Chemical Precipitation; D002850:Chromatography, Gel / Q000379:methods*; D044903:Congenital Hyperinsulinism; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007328:Insulin / Q000276:immunology; D007330:Insulin Antibodies / Q000032:analysis*; D008875:Middle Aged; D011092:Polyethylene Glycols / Q000737:chemistry
chemical_list: D007328:Insulin; D007330:Insulin Antibodies; D011092:Polyethylene Glycols