Early rapid loss followed by long-term consolidation characterizes the development of lumbar bone mineral density after kidney transplantation

Background. Bone mineral density (BMD) decreases significantly early after renal transplantation. This prospective study was designed to evaluate the longterm lumbar BMD development. Methods. Sixty-three renal-transplant recipients (mean age 44 +/- 12 years, 37 [59%] male) underwent serial yearly posttransplant laboratory parameter and BMD measurements of the lumbar spine (dual energy x-ray absorptiometry). Combined maintenance immunosuppression included prednisolone in 95% of patients. The minimum number of consecutive scans was three; the maximum number seven (n=15). Examinations were performed between 3 2 and 68 4 months posttransplant. Results. BMD was significantly lower compared with healthy controls at all times after transplantation. t scores were below -1. BMD development revealed a biphasic pattern: between 3 +/- 2 and 10 +/- 2 months, a significant BMD decrease of -0.016 +/- 0.055 g/cm(2) (-1.6%, P=0.024) occurred. Later, a moderate increase resulting in BMD stability until the sixth year post. transplant was detected. Within the first year, posttransplant osteocalcin (from 19 15 to 32: 23 mug/L) and calcitriol (from 24 +/- 15 to 43 +/- 24 ng/L) displayed a significant increase. Compared with patients with a pronounced decrease, patients with a substantial increase in early posttransplant BMD had a lower baseline BMD (0.989 +/- 0.131 vs. 1.149 +/- 0.202 g/cm(2) [P=0.0122]) and lower creatinine levels (105 +/- 23 vs. 141 +/- 53 mmol/L [P=0.0227]). Conclusion. Our study confirms a significant decrease of lumbar BMD early after renal transplantation. Bone loss was less pronounced than previously described. The longitudinal follow-up verifies a previously assumed biphasic lumbar BMD development: after the first year, no further significant bone loss occurred, and bone density remained relatively stable at significantly lower levels compared with healthy controls.