Long-Term Evaluation of Mineral Metabolism After Kidney Transplantation

Objective. Persistence of abnormalities in mineral metabolism is common after kidney transplantation and appears to have a negative effect on survival. We aimed to evaluate the mineral metabolism and identify risk factors for persistent hyperparathyroidism (HPT) over 10 years. Methods. We retrospectively analyzed the medical records of 176 consecutive renal transplant patients. Serum creatinine, calcium, phosphorus, and intact parathyroid hormone (iPTH) levels before and after transplantation up to the 10th year post transplantation were recorded for 11 different dates. Calcium > 10.2 mg/dL was considered hypercalcemia, phosphorus < 2.5 mg/dL was considered hypophosphatemia, and iPTH > 2.5 times the upper limit was considered HPT. Results. After a major fall in the first 3 months, iPTH steadily decreased over 5 years. Thereafter, it stabilized at a level of 1.5 times the upper limit. Rates of persistent HPT were 9.2% and 10.7% in the fifth and 10th years, respectively. The rate of hypercalcemia increased up to 21.7% at the ninth month, and after 10 years, it was 5.9%. The rate of hypophosphatemia peaked at 33.3% in the first month, and it was 8.9% in 10th year. Multivariate analysis revealed that calcium (P = .047) and phosphorus (P = .041) at the time of transplantation and female sex (P = .037) were independent predictors of persistent HPT in the first year. iPTH correlated significantly with kidney function and pre-transplant iPTH. Conclusions. High serum levels of iPTH, calcium, and phosphorus at the time of transplantation were risk factors for persistent HPT in kidney transplant recipients, especially when renal function was suboptimal.