Factors Influencing the Accuracy of Cortisol Secretion Rate Estimations

Abstract

A series of cortisol “secretion rates” was performed on a group of totally adrenalectomized patients maintained on cortisol (llβ,17α,21-trihydroxy-4-pregnene-3,20-dione) only. A single-injection isotope dilution technique was used, and the calculated secretion rate was compared with the known quantity of cortisol administered during the period of study. It was found that an important factor influencing the accuracy of the estimation was the rate of “secretion” on the day before the test. The results indicate that a 24-hr urine collection contains the metabolites of 70 % of the cortisol secreted during the time of study and the metabolites of 30% of the cortisol secreted during the 24 hours before the urine collection is started. Under basal conditions, this delay in the excretion of cortisol metabolites will not affect the accuracy of a cortisol secretion rate estimation, but in nonsteady-state conditions, such as adrenal hyperfunction, acute stress or during a corticotrophin stimulation test, the calculated cortisol secretion rate may not equal the quantity of cortisol secreted during the period of urine collection. Some indication of the day-to-day variation of the rate of cortisol secretion may be gained by comparing the daily excretion levels of urinary 17-OHCS. It is important always to perform an estimation of urinary 17-OHCS on the day before a secretion rate estimation and to compare the levels on the 2 days.