Clinical value of the cortisol secretion rate

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Abstract
The isotopic estimation of the cortisol secretion rate in man is now an accepted and reliable method of assaying adrenal cortical function. Seven years' experience with its clinical use is reviewed and some practical aspects of technique are considered. The mean normal resting cortisol secretion rate is 16·2 ± 5·7 mg. daily. In all of 14 cases of hypopituitarism studied secretion has been less than 2·1 mg. daily. In all of 26 cases of established Cushing's syndrome, the cortisol secretion was above 36 mg. The method can be used to follow day-by-day changes in adrenal cortisol activity and examples of such use are given. The urinary 17-ketogenic steroid excretion frequently gives results which conflict with secretion rate estimates, and can lead to erroneous clinical conclusions.