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

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).

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.

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.

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.