Sequential changes in bone biochemical parameters and bone mineral density after renal transplant

Abstract

To evaluate sequential changes in biochemical bone parameters, parathyroid hormone (iPTH), vitamin D levels and bone mineral density (BMD) over a period of 24 weeks after renal transplantation, we studied 75 patients (58 males, with a mean age of 35.4 years) who underwent their first renal transplantation without a past history of parathyroid surgery or fractures. Serum calcium, phosphorus and albumin were measured before transplant, then weekly for four weeks and monthly for the following 20 weeks. Serum iPTH and vitamin D levels and BMD were measured at baseline and 24 weeks after transplantation. After transplantation, there was a significant fall in serum calcium in the first week, followed by a gradual rise. At 12 and 24 weeks, respectively, 17.5% and 8% patients had hypercalcemia. Serum phosphorus decreased after transplant and at 24 weeks; 25% patients had hypophosphatemia. The iPTH levels declined significantly from 251 ± 218.2 pg/mL before transplant to 97 ± 142.8 pg/mL at the end of the study period. At 12 and 24 weeks, 42.7% and 51.3% patients, respectively, had persistent hyperparathyroidism (HPT). Elevated baseline iPTH levels and graft dysfunction were the risk factors for HPT at 12 weeks, while low vitamin D levels were the risk factor at 24 weeks. The BMD showed a significant decline of 2.7% after transplant, and it negatively correlated with the pre-transplant iPTH levels; the patients who received tacrolimus immunosuppression had a lower decline in BMD than the rest of the patients. No fractures were reported during the study period. We conclude that, after renal transplantation, hypercalcemia and hypophosphatemia are common, while a significant proportion of patients have persistent HPT and decline in bone mineral density.