A comparative study of urinary 17-hydroxycorticosteroids, urinary free cortisol, and the integrated concentration of plasma cortisol.

The discriminatory power of three clinical tests for adrenal activity are compared by measuring the variability of the results obtained in 40 normal control subjects, 35 patients with mild essential hypertension, and 13 patients with Cushing syndrome. The variance of the 24-h integrated plasma concentration of cortisol was significantly (P < 0.0001) smaller than the variance of the 24-h urinary excretion of 17-hydroxycorticosteroids and free cortisol. While the 24-h urinary excretion of 17-hydroxycorticosteroids and free cortisol of the patients with Cushing syndrome overlapped with the corresponding values of the normal and hypertensive subjects, their integrated cortisol concentration did not exhibit any overlap.