Using bedtime (PM) and early morning (AM) urine cortisol/creatinine ratios to evaluate pituitary-adrenal function in...

To evaluate the use of cortisol/creatinine ratios in urine specimens collected at bedtime (PM) and the following morning (AM) in a general endocrine practice as a means of assessing pituitary-adrenal function in normal volunteers, outpatients with symptoms but no clinical endocrine dysfunction, patients with Cushing syndrome, and patients with known hypopituitarism.

Double-voided PM and AM urine samples were collected from 26 healthy control subjects and 131 outpatients who had complaints of fatigue and malaise, inability to lose weight, or nonspecific concerns about potential underlying problems with their metabolism. The findings on physical examination and laboratory studies were normal in each of these outpatients. Urine was assayed for free cortisol and creatinine and expressed as ng of cortisol/mg of creatinine. Eleven patients with documented Cushing syndrome also collected urine specimens, and data for 11 patients with known hypopituitarism were also studied.

A clear diurnal pattern of low cortisol excretion at night that increased some 7-fold in the morning (P<.0001) was reproducibly identified in healthy control subjects and those outpatients with no clinical endocrine disease. In the healthy control subjects, the mean PM urine cortisol/creatinine ratio was 15.8 (95% confidence interval [CI], 12.5 to 19.0); the mean AM cortisol/creatinine was 91.5 (95% CI, 65.0 to 118.0). The mean AM/PM ratio was 6.9, and the mean difference in AM-PM was 75.7. In the outpatients, there was no significant difference in PM, AM, AM/PM, and AM-PM values in comparison with those in healthy control subjects, and no significant difference was noted in these variables among the 3 groups of outpatients (those with fatigue, weight gain, and metabolism concerns). In 11 patients with Cushing syndrome, the mean PM urine cortisol/creatinine ratio was 127.0 (95% CI, 87.0 to 166.0), and there was loss of diurnal variation with the AM/PM ratio of 1.16 (95% CI, 0.98 to 1.35). Patients with hypopituitarism had little to no increase in AM urine cortisol/creatinine in comparison with PM urine cortisol/creatinine.

Determination of PM and AM urine cortisol/creatinine ratios offers a convenient method for assessing pituitary-adrenal function.