Posttransplant bone disease: Evidence for a high bone resorption state

Loss of bone is a significant problem after renal transplant. Although bone loss in the first post transplant year has been well documented, conflicti ng data exist concerning bone loss after this time. It is equally unclear w hether bone loss in long-term renal transplant recipients correlates with b one turnover as it does in postmenapausal osteoporosis. To examine these is sues, we conducted a cross-sectional study to define the prevalence of oste oporosis in long-term (>1 year) renal transplant recipients with preserved renal function (mean creatinine clearance 73+/-23 ml/min). Bone mineral den sity (BMD) was measured at the hip, spine and wrist by DEXA in 69 patients. Markers for bone formation (serum osteocalcin) and bone resorption [urinar y levels of pyridinoline (PYD) and deoxypyridinoline (DPD)] were also measu red as well as parameters of calcium metabolism. Correlations were made bet ween these parameters and BMD at the various sites. The mean age of the pat ients was 45+/-11 years. Eighty eight percent of patients were on cyclospor ine (12% on tacrolimus) and all but 2 were on prednisone [mean dose 9+/-2 m g/day]. Osteoporosis (BMD more than 2.5 SD below peak adult BMD) at the spi ne or hip was diagnosed in 44% of patients and osteopenia was present in an additional 44%, Elevated levels of intact parathyroid hormone (i PTH) were observed in 81% of patients. Elevated urinary levels of PYD or DPD were pr esent in 73% of patients and 38% had elevated serum levels of osteocalcin, Levels of calcium, and of 25(OH) and 1,25(OH)2 vitamin D were normal. In a stepwise multiple regression model that included osteocalcin, PYD, DPD, int act PTH, age, years posttransplant, duration of dialysis, cumulative predni sone dose, smoking, and diabetes: urinary PYD was the strongest predictor o f bone mass. These results demonstrate that osteoporosis is common in long- term renal transplant recipients, The data also suggest that elevated rates of bone resorption contribute importantly to this process.