PTH and osteoporosis: Previous in vitro studies demonstrated that PTH reduces OPG gene expression in osteoblasts.16,17 In humans, serum OPG did not alter in postmenopausal women with osteoporosis after intermittent PTH 1–34 administration.18 In another study, it was stated that serum OPG did not appear to be affected in patients with PHPT.19 Two descriptive, cross-sectional researches addressed the correlation between serum OPG and PTH in healthy individuals.