Heterophile Antibody to Adrenocorticotropin Hormone Interfering with the Investigation of Cushing's Syndrome.

The practice of medicine depends on the accuracy of biochemical assays. The high prevalence of incidental masses on imaging necessitates a correct biochemical diagnosis before proceeding to radiological studies. Hormonal assays, tumour markers, and markers of cardiac injury are particularly susceptible to heterophile antibody interference which may lead to inaccurate and misleading results, inappropriate investigation and/or treatment, patient concern and potential harm. A case of heterophile antibody interference in the measurement of ACTH in a patient with Cushing's syndrome resulting in unnecessary invasive investigation is presented. Close collaboration and communication between laboratory and clinical staff is essential where laboratory results and the clinical picture are not congruent.