#2708 Impact of dialysis modality on bone phenotype

Abstract Background and Aims Literature data suggest that low bone turnover is the prevailing bone phenotype in patients treated with peritoneal dialysis (PD) and point to high sclerostin as the central culprit. Lack of adequate controls, diagnostic heterogeneity, and a changing mineral metabolism landscape and armamentarium call for a cautious interpretation and confirmation in contemporary patients. Method Laboratory parameters of mineral metabolism (biointact parathyroid hormone (PTH), fibroblast growth factor 23 [FGF23] and sclerostin), bone turnover markers (bone alkaline phosphatase [BALP], intact procollagen type I N-terminal propeptide [PINP], tartrate-resistant acid phosphatase 5b [TRAP5b]) and bone mineral density (BMD) were assessed in 636 non-diabetic kidney transplant candidates of whom 447 were treated with hemodialysis (HD) and 189 with PD. A bone biopsy was performed in 204 patients (n = 134 HD; n = 70 PD), with bone sclerostin expression assessed in a subset (n = 52). Results Patients treated with PD had lower levels of PINP (79.6 vs 99.5 ug/L; p < 0.01) and BALP (20.2 vs 23.7 ug/L; p = 0.04) compared to those treated with HD. Histomorphometric parameters of bone formation were numerically lower in patients treated with PD, but significance was not reached. Bone mineralization was impaired in HD patients (osteoid width: 7.90 vs 6.75 µM; p = 0.01; osteoid maturation: 9 vs 6 days; p = 0.03), while frank osteomalacia was rare in both modalities (6.0%, both groups). BMD was higher in patients treated with PD compared to HD at skeletal sites rich in cortical bone (Z-score midshaft radius −0.4 ± 1.3 vs −0.9 ± 1.7; p = 0.04). PTH levels were comparable (150 vs 144 pg/mL, PD vs HD), while patients treated with PD showed higher serum phosphate (4.9 ± 1.3 vs 4.5 ± 1.6 mg/dl; p < 0.01) and FGF23 levels (3852 pg/ml vs 2361 pg/ml; p = 0.01). Circulating (1.82 ng/mL, both groups) and bone tissue expression (205 ± 126 vs 206 ± 112 positive osteocytes per mm2) of sclerostin did not differ between groups. Conclusion Patients treated with PD present a lower bone turnover, better mineralization, and higher cortical BMD than counterparts treated HD. Overall, differences are marginal and most probably clinically irrelevant. We speculate that inferior phosphate control may be in the causal pathway.