TRACP‐5b/BAP Score After 3 Months of Treatment With Combined SERM/E2 Therapy Can Predict Changes in Lumbar Spine Bone Mineral Density After 1 Year of Treatment in Early Postmenopausal Osteopenia

Although changes in bone mineral density (BMD) are important indexes in osteoporosis treatment, no markers are available to predict them. Given the importance of assessing the therapeutic windows of antiresorptives, we explored potential biomarkers of bone remodeling in patients receiving treatment for osteopenia. Postmenopausal women with osteopenia (defined as a lumbar BMD T‐score <−1.0 standard deviation (SD) below that of a reference population but >−2.5 SD) were administered estradiol 1 mg/d and bazedoxifene 20 mg/d. After 3 months of treatment, we evaluated their ratio of serum bone‐specific tartrate‐resistant acid phosphatase to bone‐specific alkaline phosphatase (TRACP‐5b/BAP), which is widely used for evaluating bone turnover in postmenopausal patients with osteoporosis in Japan because their minimum significant changes are smaller than other bone turnover markers such as carboxy‐terminal collagen cross‐links (CTX) or N‐terminal propeptide of type I procollagen (P1NP) and thus, accurately reflect bone turnover. After 1 year of treatment, we assessed changes in lumbar BMD. The cut‐off TRACP‐5b/BAP scores for a ≤−2% decrease and ≥2% increase in lumbar spine BMD were 38.4 and 29.0, respectively. The TRACP‐5b/BAP scores were associated with significantly greater areas under the curve than the other evaluated parameters. These results suggest that the TRACP‐5b/BAP score after 3 months of osteopenia treatment can predict changes in lumbar BMD after 1 year of treatment. Moreover, a receiver operating characteristic curve analysis of TRACP‐5b/BAP scores after 3 months of antiresorptive therapy and percent changes in BMD at 1 year revealed that the TRACP‐5b/BAP score, as an index of the balance between bone resorption and formation markers, has the potential to serve as a modulator of the anabolic window reflective of bone remodeling. This study's findings also suggested a role for TRACP‐5b/BAP score as a predictor of a non‐response to antiresorptive therapy, thus offering health economic implications for osteoporosis treatment. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.