Plasma corticotropin radioimmunoassay, with use of fuller's earth for extraction.

A radioimmunoassay is described for plasma corticotropin whereby concentrationsover the range of 6 to 1000 ng/liter can be measured. Corticotropin extracted from plasma on fuller’s earth under carefully standardized conditions is assayed by a long-used double antibody radioimmunoassay procedure. Within (n = 6) and between (n = 12) assay precision is 39 ± 2 (SD) ng/liter and 44 ± 6 (SD) ng/liter, respectively. Normal basal corticotropin concentrations in plasma collected between 8 am. and 10 am. ranged from 6 to 68 ng/liter. Corticotropin was not detected in hypophysectomized patients and in subjects pretreated with dexamethasone, but elevated concentrations were found in an Addisonian patient and in a patient with a thymoma.