Euthyroid hyperthyroxinaemia due to endogenous antibodies to thyroxine and tri-iodothyronine. A case report.

A case of euthyroid hyperthyroxinaemia caused by auto-antibodies to thyroxine and tri-iodothyronine is presented. Gel filtration chromatography of the patient's serum showed increased binding of radio-labelled thyroxine analogue to a macromolecular component, which migrated in the gammaglobulin region on electrophoresis. Precipitation by protein A confirmed that this was an immunoglobulin. The importance of recognising this condition so that inappropriate therapy can be avoided is stressed.