Diagnostic problems caused by spurious elevation of thyrotrophin measured by sensitive assay

Thyrotrophin measured by the Amerwell immunoradiometric assay was found to be falsely elevated, causing potential diagnostic confusion in hypothyroid, euthyroid and hyperthyroid individuals. Non-specific antibodies in patients' sera may be responsible, by cross-linking the mouse monoclonal antibodies of the assay. Interference was overcome in the sera from these patients by addition of mouse serum (20 microliters per ml test serum) over and above that already incorporated in the kit. Problems with spuriously elevated thyrotrophin levels are not confined to one manufacturer's kit and can cause diagnostic confusion in several situations.