Serum Estradiol Concentration as Measured by HPLC-RIA and Bone Mineral Density in Postmenopausal Women during Hormone Replacement Therapy

OBJECTIVE: To determine the relationship between the serum estradiol concentration and bone mineral density (BMD) of the lumbar spine in postmenopausal women treated with conjugated equine estrogen (CEE) and medroxyprogesterone acetate (MPA) every other day and every day. METHODS: Eighty-four postmenopausal women were randomly treated with hormone replacement therapy (HRT) every other day and every day. Forty-seven women received oral administration of 0.625 mg CEE and 2.5 mg MPA every other day, and 37 women received oral administration of 0.625 mg CEE and 2.5 mg MPA every day. BMD of the lumbar spine at 12 months and serum concentrations of estradiol and estrone at 6 and 12 months after treatment were examined. RESULTS: The estradiol concentration in subjects treated every other day showed a significant (p < 0.001) positive correlation with the percentage change in lumbar BMD, while that in subjects treated every day was not correlated with the percentage change in BMD. The differences between serum estradiol concentrations after 12 months of treatment and initial serum estradiol values in women treated every other day and every day also showed a significant (p < 0.01 and 0.05, respectively) positive correlation with percentage changes in BMD. In women treated every other day, body mass index (BMI) in the subjects in whom BMD did not increase was significantly (p < 0.01) lower than that in the subjects in whom BMD did increase. CONCLUSIONS: The serum estradiol concentration in women treated every other day has a strong positive correlation with the percentage change in lumbar BMD, but a higher estradiol concentration may be needed for women in whom BMD did not increase with HRT every other day after due consideration of individual characteristics such as BMI.