Impact of Parathyroid Hormone on Bone Density in Long-term Renal Transplant Patients with Good Graft Function

BACKGROUND: It remains unknown whether low-grade hyperparathyroidism persisting beyond the first year postrenal transplantation has any impact on bone density. METHODS: Parathyroid hormone (PTH), glomerular filtration rate (GFR), and bone density (by dual-energy x-ray absorptiometry [DXA]) were monitored in the follow-up of our transplant patients. Of 260 long-term renal transplant patients, 41 fulfilled the following criteria: Two DXA measurements performed at least five years apart (median 6.8 years, range 5-9); GFR>or=35 ml/min per 1.73 m body surface area (median 50, range 35-76); no bisphosphonate treatment or parathyroidectomy in the study period. RESULTS: In all, 40% had mean PTH values above the normal limit 6.9 pmol/L (65 pg/ml), and the range was 0.9-17 pmol/L. In the first DXA, 8 of 41 patients had osteoporosis and 17 more had osteopenia. Hip bone density Z-score was -0.60 SD, range (-2.6 to +2.3). The absolute median value (g/cm) remained unchanged until the second DXA, but among patients there was a variation which ranged from -2.3% to +1.7% per year. In a simple linear regression analysis, these changes were significantly correlated to mean PTH (r=0.16, P=0.010). Median lumbar spine bone density was also reduced in the first DXA and was not different at follow-up, but with this variable individual changes did not correlate to mean PTH. CONCLUSION: Bone density is often reduced and PTH remains elevated in long-term renal transplant patients with good transplant function. Slight to moderate elevation of PTH is associated with reduction in hip bone mineral density.