Characterisation of an interference affecting the triiodothyronine measurement on two different immunoassays

We report a case of falsely elevated triiodothyronine (T3) due to anti-T3 antibody interference in two immunoassays (Cobas 8000 e602® module (Roche Diagnostics) and Architect® i2000 (Abbott)). The interference was investigated using various laboratory methods including the search for heterophilic antibodies, biotin detection and the polyethylene glycol precipitation of potential interfering macromolecules. The presence of anti-T3 autoantibodies was detected and measured by radioimmunoprecipitation. Our investigations confirmed the clinical suspicion of a falsely elevated free T3. No further explorations or unnecessary treatments were conducted for this patient after identification of the interference. This underlines the importance of implementing systematic analytical procedures in laboratories for the search of suspected interferences.