Early changes in bone mass, biochemical bone markers and fibroblast growth factor 23 after renal transplantation.

BACKGROUND: Serum osteocalcin and C-terminal telopeptides of type-1 collagen (CTX-1) are known markers of bone turnover, whereas the role of fibroblast growth factor 23 (FGF-23) is yet unknown. We investigated early changes in bone mass and the association of these biochemical markers and FGF-23 with bone loss following renal transplantation (RTx). MATERIAL AND METHODS: In 44 first-kidney allograft patients, BMD was measured by dual-energy X-ray absorptiometry in the lumbar spine (LS), total femur (TF) and total body (TB) at baseline and 10 weeks post-transplant. Serum osteocalcin, CTX-1, intact FGF-23, intact parathormone (iPTH) and 25-hydroxyvitamin D (25-OHD) levels were measured. Associations were tested by correlation and multiple linear regression. RESULTS: We found a significant (p<0.05) decrease in bone mass in LS (2.6 %), TF (2.1 %) and TB (1.4 %). Osteocalcin (0.95 versus 1.56 nmol/L) and CTX-1 (1.05 versus 1.47 ng/mL) levels increased significantly, while serum FGF-23 and iPTH decreased. Serum osteocalcin and CTX-1 were significantly associated at both baseline and follow-up. Baseline osteocalcin and CTX-1 were independently associated with bone loss in TB and TF, respectively. Neither iPTH nor 25-OHD showed consistent association with bone loss. FGF-23 was not related to change in bone mass or to biochemical markers of bone turnover. CONCLUSION: Our results confirm an early decrease in bone mass with high bone resorption rate after RTx. Osteocalcin and CTX-1 are associated with bone loss in the early post-transplant period; thus, these markers may be a reasonable choice for routine assessment of bone turnover in this setting. The role of FGF-23 remains to be further elucidated.

Determinants of bone mass in end-stage renal failure patients at the time of kidney transplantation.

BACKGROUND: Patients with chronic renal failure (CRF) are at high risk of renal osteodystrophy. Our study aimed to identify predictors of bone mass and cumulative fracture rate at the time of renal transplantation (RTx). This is important since the patients experience further substantial bone loss the first month post-transplant. MATERIAL AND METHODS: Altogether 133 renal transplant patients were examined for bone mineral density (BMD) using dual-energy X-ray absorptiometry shortly after RTx. RESULTS: The patients'Z-scores were significantly lower at the time of RTx compared to the reference population (p < 0.05), 32% were osteopenic and 11% had osteoporosis. Independent predictors of low bone mass were age (p < 0.001), female sex (p < 0.001), intact parathyroid hormone (iPTH) level (p < 0.001), former transplantation (p = 0.001) and time on hemodialysis (HD) (p = 0.005). Body mass index (BMI) (p < 0.001) and physical activity (p = 0.027) were associated with high BMD. Cumulative fracture rate (29%) was associated with physical inactivity (p = 0.003), BMI (p = 0.036) and osteopenia (p < 0.001) at the time of RTx. CONCLUSION: In a representative CRF population, BMD was reduced. Independent predictors of BMD were as for the general population, and uremia associated predictors were time on HD, previous transplantation and serum iPTH level. Fracture rate was high, and physical inactivity had the strongest association with fractures.