Association between bone turnover markers and bone mineral density after 12 months of exercise in patients with chronic kidney disease stages 3-5: a post-hoc exploratory sub-study of the RENEXC randomized controlled trial.

BACKGROUND: Chronic kidney disease (CKD) disrupts mineral and bone metabolism, increasing fracture risk. Exercise may improve physical performance and help preserve bone mineral density (BMD), but data on the relationship between BMD and bone turnover markers during long-term exercise in CKD are limited. We explored potential associations between intact procollagen type I N-propeptide (intact PINP), tartrate-resistant acid phosphatase 5b (TRAP5b) and BMD in CKD stages 3-5 patients completing 12 months of exercise.

METHODS: In this post-hoc, exploratory analysis of the RENEXC trial, 101 patients underwent 12 months of endurance exercise combined with strength or balance training. BMD was assessed by dual-energy X-ray absorptiometry, and plasma intact PINP and TRAP5b were measured at baseline and study end.

RESULTS: Median intact PINP and TRAP5b remained largely unchanged. In adjusted analyses including clinical, medication-related, and CKD-MBD covariates, no consistent associations were observed between bone turnover markers and BMD. ΔBMD was not associated with changes in intact PINP or TRAP5b. In multivariate models, age was the only consistent predictor of osteoporotic status across time points, while associations with intact PINP and female sex were not stable after sensitivity analyses.

CONCLUSION: In this cohort of patients with CKD stages 3-5 participating in a 12-month exercise intervention, circulating bone turnover markers (intact PINP and TRAP5b) showed minimal temporal change over 12 months and were not consistently associated with BMD or osteoporotic status after adjustment for clinical, biochemical, and treatment-related factors. Age was the only consistent variable associated with osteoporotic status across all models.