Development and evaluation of a highly sensitive and specific radioimmunoassay for measurement of adrenocorticotropin levels in plasma
MANJULA K. GUPTA, PHD
Department of Immunopathology, The Cleveland Clinic Foundation, One Clinic Center, 9500 Euclid Avenue Cleveland, Ohio 44195
TIM KOLAR, MS
LESLIE R. SHEELER, MD
The authors developed and evaluated a radioimmunoassay for adrenocorticotropin (ACTH) using Sep-Pak C18 cartridges for the extraction of the hormone prior to assay. The assay has a sensitivity of 5 pg/mL. Inter- and intra-assay coefficients of variation were 9.1 % and 4.8% at the level of 30 pg/mL (n=22). The mean ACTH level between 8 and 9 AM in 48 normal individuals was 20.3 ± 9.0 (S.D.) pg/mL with a range of 5–48 pg/mL. Mean (± S.D.) ACTH levels (8–9 AM) in nine normal subjects before and after 1 mg dexamethasone at midnight were 21 ± 8.8 and 9 ± 4.8 pg/mL, respectively, showing a mean suppression of 57 % with a range of 38–76%. ACTH levels increased two- to fivefold in five normal subjects after a single oral dose of metyrapone. In 17 patients with hypercorticolism, ACTH levels indicated the status of the pituitary-adrenal axis.