Relationship between urine and plasma estrogen ratios.

Normal young and postmenopausal women were placed into groups according to the ratio of the estrogens in their urine. Women whose ratio was greater than 1.3 if young and greater than 3.2 if postmenopausal were compared to women whose ratio was less than 0.7 and less than 2.1 for young and postmenopausal, respectively. Between the respective high- and low-ratio groups, there were no significant differences for circulating levels of estriol, metabolic clearance rates of estriol, or blood production rates of estriol, estrone, or estradiol. Women who had had breast cancer were compared to a group of normal controls and were also found to have similar blood production rates for estriol, estrone, and estradiol. The ratios of the blood production rates of estriol to estrone and estradiol were similar for the high and low groups for young and postmenopausal women and also between the breast cancer women and their controls. It appears, therefore, that the difference in urinary estrogen ratios is primarily due to different pathways of metabolism of the free circulating estrogens and not to differences in the production rates of the estrogens. Estriol is produced at only 10% the rate of estrone and estradiol.