REPRODUCIBILITY OF PLASMA-HORMONE LEVELS IN POSTMENOPAUSAL WOMEN OVERA 2-3-YEAR PERIOD

We evaluated the reproducibility of plasma hormone levels over time in 79 healthy postmenopausal women, ages 51-69 years at baseline, who we re not using postmenopausal hormones. Three blood samples were collect ed between 1989 and 1992 from each of these women. We assessed plasma levels of estradiol, free estradiol, percentage of free estradiol, bio available estradiol, percentage of bioavailable estradiol, estrone, es trone sulfate, sex hormone-binding globulin (SHBG), androstenedione, t estosterone, dehydroepiandrosterone, dehydroepiandrosterone sulfate, a nd prolactin at each of three sample collections. The means and SD for each of the plasma estrogens, SHBG, and prolactin were similar at eac h collection. For the androgens, plasma levels tended to decrease over time consistent with an aging effect; decreases with increasing age w ere statistically significant for androstenedione, dehydroepiandroster one, and dehydroepiandrosterone sulfate. Intraclass correlation coeffi cients (ICCs) ranged from 0.92 (95% confidence interval = 0.89-0.95) f or SHBG to 0.53 (95% confidence interval = 0.43-0.69) for prolactin. M ost correlations were at least 0.70, The ICCs did not vary by age or t ime since menopause. Women who changed weight over the course of the s tudy tended to have lower ICCs for a number of the hormones, although these differences were not statistically significant. These data indic ate that, for most of these plasma hormones, a single measurement can reliably categorize average levels over at least a 3-year period in po stmenopausal women.