title: A diagnostic conundrum: heterophilic antibody interference in an adrenocorticotropic hormone immunoassay not detectable using a proprietary heterophile blocking reagent.
abstract: BACKGROUND
  Heterophilic antibodies are a well-described interferent but poorly appreciated and are often not a recognized problem affecting most immunoassays. We describe for the first time heterophilic antibodies interference affecting an adrenocorticotropic hormone (ACTH) assay in a patient with Cushing's syndrome due to bilateral nodular adrenal hyperplasia.
  
  
  METHODS
  A 60-year-old retired female nurse underwent extensive invasive investigations, which were ultimately unnecessary, as a result of initial analytical interference in the ACTH assay, which could not be resolved using a proprietary heterophilic binding reagent.
  
  
  RESULTS
  This case highlights the inherent difficulty of diagnosing Cushing's syndrome and the large emphasis placed on laboratory tests. The consequence of not initially identifying interference in this patient's laboratory test results led to unnecessary and costly investigations with potentially adverse outcomes.
  
  
  CONCLUSIONS
  Clinicians and the laboratory community need to be continuously vigilant and view laboratory results with caution when they are inconsistent with the clinical picture. This approach is paramount, especially at a time of increasing automation and ever-diminishing scientist involvement in sample processing.
authors.affiliation: Department of Biochemistry, QE2 Medical Center, Nedlands, Australia. jonathan.grasko@health.wa.gov.au
authors.forename: Jonathan
authors.initials: J
authors.lastname: Grasko
authors.forename: Robin
authors.initials: R
authors.lastname: Willliams
authors.forename: Jonathan
authors.initials: J
authors.lastname: Beilin
authors.forename: Paul
authors.initials: P
authors.lastname: Glendenning
authors.forename: Soraya
authors.initials: S
authors.lastname: Fermoyle
authors.forename: Samuel
authors.initials: S
authors.lastname: Vasikaran
mesh_terms: D000312:Adrenal Hyperplasia, Congenital / Q000097:blood / Q000175:diagnosis*; D000324:Adrenocorticotropic Hormone / Q000097:blood*; D000910:Antibodies, Heterophile / Q000737:chemistry*; D003480:Cushing Syndrome / Q000097:blood / Q000175:diagnosis*; D003951:Diagnostic Errors; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000592:standards; D007202:Indicators and Reagents / Q000737:chemistry; D008875:Middle Aged
chemical_list: D000910:Antibodies, Heterophile; D007202:Indicators and Reagents; D000324:Adrenocorticotropic Hormone
keywords: Adrenocorticotropic hormone; heterophile antibodies; immunoassay