Parameters of high bone-turnover predict bone loss in renal transplant patients: A longitudinal study

Background. Osteoporosis is a serious complication of kidney transplantatio n. Various factors have been postulated to contribute to posttransplant bon e loss, among them treatment with corticosteroids, the use of cyclosporine and cyclosporine-like agents, and persistent hyperparathyroidism. In a prev ious cross-sectional study of long-term renal transplant recipients, we obs erved that osteoporosis or osteopenia was present in 88% of patients. Becau se biochemical markers of bone formation (serum osteocalcin) and bone resor ption (urine pyridinoline, PYD, and deoxypyridinoline, DPD) were elevated i n the majority of study subjects, we hypothesized that elevated rates of bo ne-turnover contribute to posttransplant bone loss in long-term renal trans plant patients. This study was performed to examine this hypothesis. Methods. The study population was composed of 62 patients who were more tha n 1-year postrenal transplantation and who had preserved renal function, Th ey were followed prospectively for 1 year. Biochemical markers of bone-turn over were measured at study entry, and patients were classified as having h igh bone-turnover based on elevated urinary levels of at least one marker o f bone resorption (i,e,, PYD or DPD) and/or serum osteocalcin (group i), If none of these were present, they were classified as having normal bone-tur nover (group 2), Bone mineral density (BMD) was measured by dual energy x-r ay absorptiometry (DEXA) at time of entry into the study and again after 1 year of follow-up, The changes in BMD at the lumbar spine, hip, and wrist o ver the period of the study were compared between the high and normal bone- turnover groups. Results Forty-three patients (69%) were classified as having high bone-turn over (Group 1), and 19 patients (31%) were classified as having normal bone -turnover (Group 2), There was a statistically significant difference in ch ange in BMD between the two groups at the lumbar spine (-1.11 +/-0.42%, hig h bone-turnover, vs. 0.64 +/-0.54%, normal bone-turnover; P=0.02) and the h ip (-0.69 +/-0.38%, high bone-turnover, vs. 1.36 +/-0.66%, normal bone-turn over; P=0.006). Whereas group 2 had stable bone mass, group 1 exhibited bon e loss at these skeletal sites. Conclusions. Our results indicate that bone loss is greater in renal transp lant recipients with elevated biochemical markers of bone-turnover, suggest ing that these markers may be useful in identifying patients at risk for co ntinued bone loss. These data support the hypothesis that continued bone lo ss in longterm renal transplant recipients is associated with high bone-tur nover. If accelerated bone resorption does play a role in posttransplant bo ne loss, this would provide a strong rationale for use of antiresorptive th erapy for the prevention and treatment of this complication.