Corticotropin hormone assay interference: A case series

Measuring the plasma corticotropin (ACTH) concentration is an important step in determining the underlying cause in patients with hypercortisolemia. Interfering substances in immunoassays can lead to erroneous results impacting clinical management. We describe a case series of 12 patients, the majority of whom were being investigated for possible Cushing's syndrome and in whom inconsistencies between the clinical picture and biochemical testing raised concerns of assay interference. ACTH assay interference resulted in falsely elevated ACTH concentrations using the Siemens Immulite assay and consequently led to additional unnecessary testing. Communication between physician and laboratory as well as appropriate investigation (including sample dilution, use of blocking antibodies and testing on an alternate platform) resulted in assay interference identification. Recognition of biochemical results which are clinically discrepant remains an essential step in patient assessment.