title: The hook effect in calcitonin immunoradiometric assay: a case report.
abstract: The hook effect, which has long been detected and documented for immunoradiometric assays (IRMA) such as those measuring prolactin or thyroglobulin, occurs when the serum antigen level is extremely high, thus inducing a bias in the methodology of measurement.
  
  
  RESULTS
  We report the case of an 80-year-old man with confirmed medullary thyroid carcinoma (MTC). In the case reported here, the clinical status of the patient contrasts with his tumor antigen, serum calcitonin (CT), concentrations. The measured increased CT concentrations revealed the presence of a hook effect. This phenomenon occurs due to an excess of antigen during the one-step IRMA where the signal antibodies, bound to the non-captured antigens, are washed out during the measurement, inducing the loss of signal. Aiming to prevent the "hook effect", successive dilutions of the same sample of serum were done.
  
  
  CONCLUSIONS
  Previous studies have shown when one-step IRMA reveals high concentrations of a tumor serum antigen (i.e. prolactin or thyroglobulin), a two-step IRMA or a systematic 1:10 dilution of the serum sample prevents the formation of the "hook effect". In our case report, the CT "hook effect" formation was prevented by performing serial dilutions of the serum sample.
authors.affiliation: Department of Biochemistry and Pharmaco-Toxicology, hôpital de la Cavale-Blanche, CHRU, boulevard Tanguy-Prigent, 29609 Brest cedex, France.
authors.forename: Marie-Sarah
authors.initials: MS
authors.lastname: Fangous
authors.forename: Hélène
authors.initials: H
authors.lastname: Kerspern
authors.forename: Marie-Pierre
authors.initials: MP
authors.lastname: Moineau
authors.forename: Véronique
authors.initials: V
authors.lastname: Kerlan
authors.forename: Zarrin
authors.initials: Z
authors.lastname: Alavi
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Carré
mesh_terms: D000369:Aged, 80 and over; D016477:Artifacts; D002116:Calcitonin / Q000032:analysis / Q000097:blood* / Q000502:physiology*; D018278:Carcinoma, Neuroendocrine; D006801:Humans; D015592:Immunoradiometric Assay / Q000379:methods / Q000592:standards; D008297:Male; D009994:Osmolar Concentration; D013964:Thyroid Neoplasms / Q000097:blood* / Q000175:diagnosis; D017186:Titrimetry
chemical_list: D002116:Calcitonin