Mineral Metabolism Markers Are not Associated with Renal Transplant Outcomes

Abstract

Hyperparathyroidism is a complication of chronic renal failure. A functioning kidney graft improves hyperparathyroidism but it still persists to some degree. In addition hypercalcemia, hypophosphatemia, renal phosphate wasting and hypercalciuria are common after kidney transplantation. Some authors have reported an association of serum phosphate and calcium concentrations with renal transplant outcomes but information about the effects of parathyroid hormone levels is not given. The purpose of the present work was to assess the association between calcium phosphate mineral metabolism markers and graft outcomes. Patients and methods: From 389 renal transplants performed in our center between January 2000 and June 2008, 331 patients, 204 males and 127 females, with a mean age at transplantation of 52.2±14.0 years and with a functioning graft at 12 months were included in the study. All of them have measurements of intact parathyroid hormone (iPTH), serum calcium and phosphate, tubular phosphate reabsorption and urinary calcium excretion at 1, 3, 6 and 12 months. Graft and patient surival and ocardiovascular events were collected from an electronic data base. The mean follow-up was of 84.0±31.8 months Results: At 1 months 42 patients (12.6%) had normal levels of iPTH (< 70 pg/ml), 96 patients (28.9%) had iPTH levels between 70 and 150 pg/ml, 91 patients (27.7%) had iPTH levels between 150 and 300 ng/ml and 102 patients had iPTH levels >300 pg/ml. iPTH levels decreased from 265±263 pg/ml at 1 months to 165±134 pg/ml at 12 months (p=0.000) and only 45 patients (13.6%) had iPTH levels > 300 pg/ml (p=0.000). About 18% of patients had serum phosphate concentrations >3.5 mg/dl and about 10% of patients had adjusted serum calcium >10.5 mg/dl at 6 and 12 months. The calcium phosphate product was >35 in 53 patients (16.0 %) at 6 months and in 57 patients (17.2%) at 12 months. During the follow-up period, 63 grafts (19.0%) were lost and 30 patients (9.0%) died and 80 recipients (24.1%) presented at least one cardiovascular event. According to univariate Cox proportional analysis, high iPTH levels at 1 month after transplantation were not associated with worse patient (p=0.413), with graft survival (p=0.391) or with a higher risk of cardiovascular events (p=0.111). There was no relationship between iPTH levels at 1 month and serum creatinine at 1, 2 and 3 years. Serum calcium and phosphate concentrations and calcium phosphate product at any time during the first year after transplantation were not associated with graft and patient outcomes or cardiovascular events. Conclusions: Abnormalities of mineral metabolism are common in the first year after transplantation. iPTH levels and serum phosphate concentrations and calcium phosphate product during the first year after transplantation were not associated with graft outcomes.