Measurement of plasma adrenocorticotropic hormone, or ACTH, is key in the differential diagnosis of hypothalamic pituitary adrenal disorders. Two-site sandwich immunoassay dominate clinical testing of ACTH in North America.  However, discordant results among different assays have been repeatedly reported.  To help resolve this discrepancy, a multicenter effort developed a liquid chromatography tandem mass spectrometry assay for the intended measurand, that is the biologically active intact ACTH.  A report on that initiative appears in the November 2019 issue of Clinical Chemistry.  We are pleased to have the senior author of that paper , Dr. Mari DeMarcoas our guest in this podcast.