LABORATORY REPRODUCIBILITY OF ENDOGENOUS HORMONE LEVELS IN POSTMENOPAUSAL WOMEN

We conducted several studies to assess the ability of laboratories to reproducibly measure plasma levels of estrone, estradiol, percent free estradiol, sex hormone binding globulin, dehydroepiandrosterone sulfa te, androstenedione, testosterone, progesterone, follicle-stimulating hormone, and prolactin in postmenopausal women. We sent four to seven replicate samples of plasma to each of four well-established endocrine laboratories in the United States on one or two separate occasions. A ll replicate samples were handled identically during processing, stora ge, and retrieval, and were labeled to preclude their identification b y the receiving laboratory. The within-person coefficient of variation , a measure of laboratory error, was consistently low (<15%) for folli cle-stimulating hormone and prolactin. For estrone and estradiol, horm ones present at low levels in postmenopausal women, the laboratory err or was often large (>25%) and the ratio of between-person variation to laboratory error was often less than 2.0. Reproducibility of androste nedione, dehydroepiandrosterone sulfate, testosterone, progesterone, s ex hormone binding globulin, and percent free estradiol was also varia ble. Our results emphasize the need for evaluating laboratory performa nce before sending samples for hormone analysis and for increased coll aboration between epidemiologists and laboratory investigators in impr oving hormone measurements for use in epidemiological research.