Rapid radioimmunoassay for corticotropin in unextracted human plasma.

This RIA for corticotropin (ACTH) involves use of a commercially available antiserum and permits measurement of immunoreactive ACTH in unextracted plasma. The assay takes 2.5 days, detects as little as 5 pg/mL of plasma, and is specific: structurally and (or) biosynthetically related peptides do not cross react. Generally, data on dilutions of almost all human plasma specimens produce curves parallel to that for the ACTH reference standard. Values correlate well with those obtained by a well-established but more laborious RIA. We measured immunoreactive ACTH in normal subjects at various times of the day and after modulation of their pituitary-adrenal axis, and in patients with hypo- and hyper-secretion of ACTH. We conclude that the full range of immunoreactive ACTH values, which accurately reflect the status of the subject's pituitary-adrenal axis, can be quickly and easily determined in samples of unextracted human plasma.