Serum cortisol levels via radioimmunoassay vs liquid chromatography mass spectrophotometry in healthy control subjects and patients with adrenal incidentalomas

Background: Adrenal incidentalomas (AIs) are present in 4% of adults. As many as 30% may secrete cortisol autonomously in the absence of specific signs of overt hypercortisolism, in a phenomenon called subclinical hypercortisolism (SH). Diagnosis of SH is established by serum cortisol resistance to dexamethasone suppression. Methods: We compared serum cortisol concentrations, as determined by radioimmunoassay (RIA) and liquid chromatography/ tandem mass spectronomy (LC/MS-MS), in 73 patients with AI group (52 with unilateral AI) and 34 control subjects in 3 scenarios: basal; after 1-mg dexamethasone suppression; and after 0.25-mg stimulation with cosyntropin, a synthetic derivative of adrenocorticotropic hormone (ACTH). To bolster evidence for the diagnosis of SH, we also measured salivary cortisol levels at 11 PM and after DST, as well as plasma ACTH and serum dehydroepiandrosterone sulfate (DHEA-S) levels. Results: We observed significant positive correlation (r = 0.9345, P <.001) for all 318 pairs of serum cortisol values, as measured by both methods. Conclusions: Serum cortisol concentrations in patients with AI and in control subjects were very similar, as measured by RIA and LC/MS-MS.