title: [False results on elevated triiodothyronine values in radioimmunoassay].
abstract: Five patients with falsely elevated serum triiodothyronine (T3) concentrations (> 9 nmol/l) in a radioimmunoassay are reported. The high T3-values disagreed with the other thyroid variables investigated as well as with the clinical observations. In sera from all patients a normal non-specific binding of T3 was found, thus excluding abnormal serum-protein-binding of the hormone. An ethanol extraction of T3 from serum before RIA reduced the T3 content in serum from all patients to normal levels (2.0-2.4 nmol/l). These findings indicate the presence in the sera of substances, probably of protein nature, that were interfering with the assay by binding the reagent-antibody and not the antigen. Addition of non-immune rabbit serum prevented this interference and normalized the T3-values (1.8-2.4 nmol/l). Thus the interfering substance in T3-RIA could be an anti-rabbit antibody, the interaction of which can be eliminated by a minor modification of the assay making it possible to differentiate true from false T3-values.
authors.affiliation: Medicinsk endokrinologisk afdeling F. Amtssygehuset i Herlev.
authors.forename: L
authors.initials: L
authors.lastname: Skovsted
authors.forename: J E
authors.initials: JE
authors.lastname: Hansen
authors.forename: B
authors.initials: B
authors.lastname: Nygaard
mesh_terms: D000328:Adult; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D008297:Male; D011863:Radioimmunoassay; D014284:Triiodothyronine / Q000097:blood*
chemical_list: D014284:Triiodothyronine
vernacular_title: Falsk forhøjelse af trijodtyroninvaerdier ved radioimmunanalyse.