title: Thyroxin overdose due to rheumatoid factor interferences in thyroid-stimulating hormone assays.
abstract: BACKGROUND
  Immunoassays are susceptible to interferences by anti-hormone antibodies, heterophilic antibodies or rheumatoid factor (RF).
  
  
  METHODS
  We report a case of levothyroxin overdose because of gross overestimation of thyroid-stimulating hormone (TSH) by chemiluminescent and IRMA assays. Alternate assays were performed and heterophilic antibodies blocking tubes were used.
  
  
  RESULTS
  Analytical investigations revealed: i) non-linear concentrations of TSH after serum dilutions, ii) decreased TSH concentrations after removal of heterophilic antibodies, iii) appropriately decreased TSH concentrations in alternate TSH assays and iv) identification of increased concentrations of RF.
  
  
  CONCLUSIONS
  The presence of RF may be responsible for false determination of TSH concentrations preventing monitoring of TSH.
authors.affiliation: Department of Nuclear Medicine, University Hospital and University Bordeaux, Pessac, France.
authors.forename: Agnès
authors.initials: A
authors.lastname: Georges
authors.forename: Anne
authors.initials: A
authors.lastname: Charrié
authors.forename: Sophie
authors.initials: S
authors.lastname: Raynaud
authors.forename: Christine
authors.initials: C
authors.lastname: Lombard
authors.forename: Jean-Benoît
authors.initials: JB
authors.lastname: Corcuff
mesh_terms: D016477:Artifacts; D062787:Drug Overdose; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D008297:Male; D008875:Middle Aged; D012217:Rheumatoid Factor / Q000276:immunology*; D013972:Thyrotropin / Q000032:analysis* / Q000276:immunology; D013974:Thyroxine / Q000009:adverse effects*
chemical_list: D013972:Thyrotropin; D012217:Rheumatoid Factor; D013974:Thyroxine