Circadian Cycle of Urinary Cortisol in Healthy Subjects and in Cushing's Syndrome1

The diurnal variation of unconjugated urinary cortisol was measured in 12 healthy subjects and in 3 patients with Cushing's syndrome secondary to adrenal hyperplasia. A sensitive double isotope dilution assay has allowed the quantitation of cortisol in 5 ml urine aliquots with satisfactory precision and accuracy. A circadian variation was present in the normal subjects withpeaks in the early or late morning hours and minima in the late evening hours; this rhythm is consistent with the known diurnal changes of plasma cortisol. A cycle was also present in 3 patients with Cushing's syndrome secondary to adrenal hyperplasia; its deviations from the normal pattern are pointed out in the text.