Metabolic Evaluation of Kidney Transplant Recipients for Stone Disease and Comparison with Healthy Controls and Stone Formers

Abstract

Objective The aim of this study was to determine the metabolic effects of kidney transplantation and calcineurin inhibitors (CNIs) on stone formation in the post-transplant period. Materials and Methods Forty kidney transplant recipients (KTRs) and 40 patients undergoing percutaneous nephrolithotomy (PNL) operation due to kidney stone disease between January 2002 and January 2010 were evaluated retrospectively. For control group 20 patients who neither had urinary stone disease (USD) nor a kidney transplant were chosen. Results No statistical difference was observed in terms of age, gender, body-mass index (BMI) and urinary pH between the groups. Twenty-four hour urine volume was significantly higher in the KTRs (p=0.001). However 24 hour urinary oxalate, citrate, uric acid, sodium and calcium levels were lower in the KTRs when compared to two other groups (p=0.001, p=0.0001, p=0.004, p=0.046, p=0.017, respectively). Twenty-four hour urinary potassium levels in the control group and the phosphorus levels in the group undergoing percutaneous nephrolithotomy were higher compared to other groups (p=0.022, p=0.008). After follow-up of 23.55 +/- 14 (2-50) months none of the KTRs were diagnosed with a urinary stone. Conclusion Although no stones were detected in the transplant group, low levels of urinary citrate may lead to de novo stone formation in the longer follow-up. Low levels of urinary calcium, oxalate, phosphate, uric acid and increased urine volume may axplain the fact that no stone was detected in this group. CNIs may increase metabolic tendency to stone formation in addition to their nephrotoxic effects. However our data does not support routine citrate replacement therapy for preventing stone formation and minimizing the toxic effects of CNIs due to tubular acidosis.