Mineral and bone disorder after kidney transplantation

Abstract

After successful kidney transplantation, accumulated waste products and electrolytes are excreted and regulatory hormones return to normal levels. Despite the improvement in mineral metabolites and mineral regulating hormones after kidney transplantation, abnormal bone and mineral metabolism continues to present in most patients. During the first 3 mo, fibroblast growth factor-23 (FGF-23) and parathyroid hormone levels decrease rapidly in association with an increase in 1,25-dihydroxyvitamin D production. Renal phosphate excretion resumes and serum calcium, if elevated before, returns toward normal levels. FGF-23 excess during the first 3-12 mo results in exaggerated renal phosphate loss and hypophosphatemia occurs in some patients. After 1 year, FGF-23 and serum phosphate return to normal levels but persistent hyperparathyroidism remains in some patients. The progression of vascular calcification also attenuates. High dose corticosteroid and persistent hyperparathyroidism are the most important factors influencing abnormal bone and mineral metabolism in long-term kidney transplant (KT) recipients. Bone loss occurs at a highest rate during the first 6-12 mo after transplantation. Measurement of bone mineral density is recommended in patients with estimated glomerular filtration rate > 30 mL/min. The use of active vitamin D with or without bisphosphonate is effective in preventing early post-transplant bone loss. Steroid withdrawal regimen is also beneficial in preservation of bone mass in long-term. Calcimimetic is an alternative therapy to parathyroidectomy in KT recipients with persistent hyperparathyroidism. If parathyroidectomy is required, subtotal to near total parathyroidectomy is recommended. Performing parathyroidectomy during the waiting period prior to transplantation is also preferred in patients with severe hyperparathyroidism associated with hypercalcemia.

Keywords: Bone mineral density; Phosphatonin; Phosphaturia; Renal transplantation; Tertiary hyperparathyroidism.

Figure 1

Serum calcium (mean ± SD) (A) and serum phosphate (mean ± SD) (B) in chronic kidney disease patients and kidney transplant recipients according to chronic kidney disease stages, intact parathyroid hormone levels [median (interquartile range)] in chronic kidney disease patients and kidney transplant recipients according to chronic kidney disease stages[8] (C). ^aP < 0.05 vs CKD, ^bP < 0.001 vs CKD. CKD: Chronic kidney disease; KT: Kidney transplant.

Figure 2

Total vascular calcification scores of chronic kidney disease stages 5D patients and kidney transplant recipients categorized according to (A) dialysis vintage (B) kidney transplant vintage. Total VC scores are expressed as mean ± SE[60]. ^aP < 0.05 vs CKD. VC: Vascular calcification; KT: Kidney transplant; CKD: Chronic kidney disease.