Endocrine Abstracts

Background: Bone is constantly remodelling and an imbalance between bone resorption and formation can predispose to osteoporosis. Bone turnover markers (BMTs) are biochemical markers that reflect the dynamics of bone formation and resorption. Carboxy-terminal collagen crosslinks (CTx) is a bone resorption marker measured in serum which is used to monitor treatment response.

Aims: The aims of the study were to determine how CTx has been used to monitor patients following treatment with intravenous zoledronic acid and denosumab at Queen Elizabeth Hospital Birmingham and to assess the performance of bone turnover markers in clinical practice by assessing their use in monitoring treatment response.

Methods: Retrospective analysis of patient’s records who completed a full course of zoledronic acid (n=77) or denosumab (n=36). Significant treatment response was defined as a reduction of the CTx concentration by more than 30% from baseline or post-treatment values in the lower half of the pre-menopausal range (<0.3 ng/ml) if no baseline measurements were present.

Results: For the zoledronic acid group, 60 patients (78%) had CTx measurements pre- and post-treatment or post-treatment only. Of these patients, 61% of patients showed a significant treatment response. Mean serum CTx pre-treatment was 0.34 ng/ml, falling to 0.21 ng/ml post-treatment (P=0.05). 30 patients (91%) in the denosumab groups had CTx measurements pre- and post-treatment or post-treatment only. 65% of these patients showed a significant treatment response. Mean serum CTx pre-treatment was 0.34 ng/ml, falling to 0.18 ng/ml post-treatment (P=0.01).

Conclusions: Following a full course of treatment serum CTx values decreased by 37% in the zoledronic acid group and 53% for the denosumab group. It remains to be seen whether those with significant reductions in CTx have lower fracture incidence. The study highlights that BMTs can be a useful measure of treatment response in clinical practice. Further follow up is required to assess impact on clinical outcomes.