A Pseudo-Hyper Triiodothyroninemia Caused by Heterophile Antibodies Interference in Radio Immunoassay

Since mouse antibodies are commonly used in diagnostic kits, their presence including auto antibodies/heterophile antibodies in some patients' sera has been known as a potential source of interference and false immunoassay results for a long time. This is a case report of a 49 year-old woman presenting with nonspecific symptoms suspected to hyperthyroidism. Her total triiodothyronine (T3) test was more than twice of the expected value, exclusively by radio immunoassay (RIA) method. Interferences due to the protein binding disorders was ruled out using radio-labeled T3, binding to the separated binding proteins by electrophoresis. Presence of auto antibody ruled out by a manual (in house) method. In this manual method, anti human IgG and IgM coated wells used for auto antibody stripping. In addition animal serum used as blocking reagent. Precipitating technique by polyethylene glycol (PEG) showed a false-positive result in T3 assay caused by a heterophile IgG class antibody. In our review of literatures, so far, this is the first case report of false-positive interference, exclusively in total T3 assay due to Heterophile antibody.