Abstract
The proper clinical evaluation of pituitary and adrenal disorders depends on the accurate measurement of plasma ACTH. The modern two-site sandwich ACTH immunoassay is a great improvement compared with older methods but still has the potential for interferences such as heterophile antibodies and pro-opiomelanocortin (POMC) and ACTH fragments. We report the cases of five patients in whom the diagnosis or differential diagnosis of Cushing syndrome was confounded by erroneously elevated results from the Siemens ACTH Immulite assay [ACTH(Immulite)] that were resolved using the Roche Cobas or Tosoh AIA [ACTH(Cobas) and ACTH(AIA), respectively]. In one case, falsely elevated ACTH(Immulite) results owing to interfering antibodies resulted in several invasive differential diagnostic procedures (including inferior petrosal sinus sampling), MRI, and unnecessary pituitary surgery. ACTH(Cobas) measurements were normal, and further studies excluded the diagnosis of Cushing syndrome. In three cases, either Cushing disease or occult ectopic ACTH were suspected owing to elevated ACTH(Immulite) results. However, adrenal (ACTH-independent) Cushing syndrome was established using ACTH(AIA) or ACTH(Cobas) and proved surgically. In one case, ectopic ACTH was suspected owing to elevated ACTH(Immulite) results; however, the ACTH(Cobas) findings led to the diagnosis of alcohol-induced hypercortisolism that resolved with abstinence. We have concluded that ACTH(Immulite) results can be falsely increased and alternate ACTH assays should be used in the diagnosis or differential diagnosis of clinical disorders of the hypothalamic-pituitary-adrenal axis.