Reproducibility of plasma and urinary sex hormone levels in premenopausal women over a one-year period

Although endogenous sex steroid hormones in premenopausal women may be asso ciated with the risk of breast cancer and other illnesses, direct evidence to support this hypothesis is limited in large part by methodological issue s in the conduct of relevant studies. One major unresolved issue is whether a single blood sample (such as is available in most epidemiological studie s), collected in a specific phase of the menstrual cycle, reflects long-ter m levels in that phase. To address this issue, two sets of blood and urine samples were obtained from 87 premenopausal women over a 1-year period in b oth the follicular and luteal phases. Plasma estradiol, estrone, and estron e sulfate were measured in the blood samples obtained in both phases, where as progesterone and urinary 2- and 16 alpha-hydroxyestrone were measured in luteal-phase samples only. For all of the women combined, intraclass corre lation coefficients (ICCs) ranged, with one exception, from 0.52 to 0.71 fo r the plasma estrogens and the urinary estrogen metabolites. The sole excep tion was for estradiol in the luteal phase (ICC = 0.19); inclusion of only women who were ovulatory in both cycles and who collected each sample 4-10 days before their next period resulted in a substantially higher ICC for es tradiol in the luteal phase (ICC = 0.62; 95% confidence interval, 0.43-0.78 ), These data indicate that, for several plasma and urinary sex hormones, a single follicular- or luteal-phase measurement in premenopausal women is r easonably representative of hormone levels in that phase for at least a 1-y ear period.