Associations of Changes in Bone Turnover Markers with Change in Bone Mineral Density in Kidney Transplant Patients

Background Bone loss after kidney transplantation is highly variable. We investigated whether changes in bone turnover markers associate with bone loss during the first post-transplant year. Methods Bone mineral density (BMD) was measured at 0 and 12 months, with biointact parathyroid hormone, bone-specific alkaline phosphatase (BALP), intact procollagen type I N-terminal propeptide (PINP), and tartrate-resistant acid phosphatase isoform 5b (TRAP5b) measured at 0, 3, and 12 months post-transplant (N=209). Paired transiliac bone biopsies were available in a subset (n=49). Between-group differences were evaluated by Student's t test, Wilcoxon signed-rank test, or Pearson's chi-squared test. Results Changes in BMD varied from -22% to +17%/yr. Compared with patients with no change (+/- 2.5%/yr), patients who gained BMD had higher levels of parathyroid hormone (236 versus 136 pg/ml), BALP (31.7 versus 18.8 mu g/L), and Intact PINP (121.9 versus 70.4 mu g/L) at time of transplantation; a greater decrease in BALP (-40% versus -21%) and Intact PINP (-43% versus -13%) by 3 months; and lower levels of Intact PINP (36.3 versus 60.0 mu g/L) at 12 months post-transplant. Patients who lost BMD had a less marked decrease, or even increase, in Intact PINP (+22% versus -13%) and TRAP5b (-27% versus -43%) at 3 months and higher Intact PINP (83.7 versus 60.0 mu g/L) and TRAP5b (3.89 versus 3.16 U/L) at 12 months compared with patients with no change. If none of the biomarkers decreased by the least significant change at 3 months, an almost two-fold (69% versus 36%) higher occurrence of bone loss was seen at 12 months post-transplant. Conclusions Bone loss after kidney transplantation was highly variable. Resolution of high bone turnover, as reflected by decreasing bone turnover markers, associated with BMD gain, while increasing bone turnover markers associated with bone loss.