Clinical Evaluation of Urinary Cortisol Determinations by Competitive Protein-Binding Radioassay

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Abstract
Urinary cortisol determinations were carried out on samples from 162 subjects by a method described previously. After extracting the cortisol from 1 ml or less of a 24-hr urine volume into methylene chloride, it was measured according to its competition with tritiated cortisol for binding sites on the corticosteroid-binding globulin of human plasma. Values in healthy subjects (48 ± 32 μg/24 hr with a range of 0 to 108 μg/24 hr) did not differ significantly from those found in obese, chronically ill and hypertensive patients. All 32 values found in 14 cases of Cushing's syndrome exceeded 120 μg/24 hr. Subjects in whom adrenocortical secretion was suppressed by dexamethasone or who were known to have adrenocortical hypofunction had very low values (3±6 μg/24 hr). This determination can be carried out in 2–3 hr and is highly specific for cortisol. It is particularly useful clinically for the detection of adrenocortical hyperfunction.