big ACTH

big ACTH

a form of poorly processed ACTH produced by certain tumors, which is a larger and more acidic peptide molecule than little ACTH, but is not immunochemically distinguishable from it and does not exert any of the biologic effects characteristic of ACTH proteolytic digestion of big ACTH yields hormonally active little ACTH.
References in periodicals archive ?
Several laboratory findings could have been erroneously attributed to 2 phenomena, "big ACTH" and complexes of ACTH with immunoglobulin, that occur in patients with ACTH-secreting tumors and affect measurement of ACTH.
Moreover, "big ACTH" is measured by some assays (notably RIAs) and not by others (1).