Role of Bone Turnover Markers and Bone Mineral Density in Monitoring Bone Health at One- and Three-Year Post-antiresorptive Therapy Initiation in Patients With Osteoporosis: A Retrospective Cohort Study

Background The gold-standard assessment of bone health is bone mineral density (BMD) measurement using dual-energy X-ray absorptiometry (DEXA); however, this modality is limited in its ability to detect short-term changes. Bone turnover markers (BTMs), specifically serum C-terminal telopeptide of type I collagen (CTX) and procollagen type I N-terminal propeptide (P1NP), offer the advantage of more frequent monitoring, yet their reliability as surrogate markers of bone health remains uncertain. This study investigates the relationship between BTMs and BMD during osteoporosis treatment. Methods Records of 214 patients treated at the Central Coast Osteoporosis Refracture Prevention (ORP) Clinic between June 2018 and May 2023 were reviewed. The relationship between BMD change (∆BMD) and changes in the levels and ratio of BTMs (∆BTM), specifically the propeptide of type I procollagen (P1NP) and the b-C-terminal telopeptide of type I collagen (CTX), at one-year and three-year post-treatment initiation was assessed. Simple statistical analysis and evaluation of the correlation coefficient were performed, including group stratification into clinically stable and clinically positive ∆BMD. A secondary analysis also stratified patients into those treated with IV versus oral bisphosphonates, using analysis of variance to compare the average change in BTM. Results Correlations between ∆BMD at all sites and ∆BTMs or the P1NP:CTX ratio were weak and not significant at one year. BTMs generally decreased with BMD improvement. There was no significant difference in BTM change over one to three years between patients with BMD improvement and those with BMD stability. However, ∆CTX was significantly greater in the improvement group in zoledronic acid (ZA)-medicated patients. These patients also had significant BMD changes at the hip and spine. ∆BTMs reached the clinical least significant change (LSC) with both medications. Conclusions Changes in BTMs and the P1NP:CTX ratio appear poorly correlated with medium- to long-term BMD changes. BTMs could potentially indicate therapeutic efficacy early in treatment, CTX perhaps more reliably than P1NP. Attainment of the LSC may more accurately predict BMD improvement than the magnitude of ∆BTMs. ZA may improve BMD more than oral bisphosphonates.