Erroneous plasma "cortisol" values in Addison's disease : A problem of the fluorimetric assay of 11-OH corticosteroids.

A case is described in which a woman, being investigated for Addison's disease, had what appeared initially to be plasma cortisol levels within the normal range. Subsequent investigations including ACTH stimulation and an immunofluorescent test for adrenal cortical antibodies showed the diagnosis to be correct. Attention is drawn to the lack of specificity of the fluorimetric plasma 11-OH corticosteroid assay and, therefore, to the danger of using plasma "cortisol" as a screening test for adrenocortical hypofunction.