Background: In successful renal transplantation, the degree of renal function recovery is usually incomplete and information is scarce about the abnormalities of mineral metabolism in long-term adult renal recipients with normal renal function. This study was designed to investigate bone mineral metabolism in patients with a long-term normal functioning kidney.
Methods: Twenty-nine adult asymptomatic renal transplant (RT) recipients with stable graft function for more than 10 years and serum creatinine <2 mg/dL were studied. They were classified into two groups according to glomerular filtration rate: Group A (N = 12; nine men, three women)>70 mL/min (x: 126 +/- 55 mL/min) and Group B (N = 17; nine men, eight women) <70 mL/min (x: 56 +/- 11 mL/min). Circulating biochemical markers of bone remodelling, bone histomorphometry, and densitometry (lumbar spine and hip) were obtained to investigate bone disease in these patients.
Results: Serum PTH was slightly elevated in 10 patients (83%) in group A. Serum PTH levels were positively related to serum calcium, osteocalcin, BAP, telopeptide, OH-proline, and creatinine. There was no histologic data to support overactivity on bone in this group of patients, with only one showing high bone turnover. Mineralization was prolonged in 34% of patients. Twenty-two patients (75%) exhibited normal bone turnover. In the group with GFR>70 mL/min the prevalence of mineralization defect in the presence of normal serum levels of calcitriol suggested vitamin D resistance. Lumbar and femoral neck osteoporosis was present in 25% and 33% of patients in group A, and 23% and 53% in group B, respectively. T-score at lumbar spine was negatively correlated with months since transplantation. Patients under treatment with cyclosporine (CsA) showed increased concentrations of osteocalcin and D-pyr and higher lumbar bone mineral density (BMD), but bone histomorphometry was not influenced by CsA.
Conclusion: Patients with long-term renal transplantation with normal renal function frequently present with slight increases in PTH, but without an effect on bone histology. CsA did not induce changes in bone histology and delayed mineralization was frequently observed.