Background: After the initial period of kidney transplantation, the prevalence of proximal tubular dysfunction (PTD) and its consequences are unknown. The aim of this study was to evaluate PTD prevalence in kidney transplant recipients, after the first year, and to analyze its risk factors. Methods: We conducted an observational and cross-sectional study between April 2012 and April 2013 at Limoges university hospital (France). The inclusion criteria were : kidney transplantation for at least one year, and eGFR [MDRD] > 15 mL/min/1,73m². PTD was assessed by the association of urine cystatin C (UCC)/urine creatinine > 20 ¯o;g/mmol and UCC > 100 ¯o;g/L. Results: 356 patients were included, among them 335 could have a full analysis (64.8% males and 35.2% females, with a mean age of 57.8 years (20.0 to 84.4)). 92.9% of patients were treated with calcineurin inhibitors, (Cyclosporine (CsA) : 51.6%, Tacrolimus (Tac) : 41.3%), 81.8% with anti-metabolites (Azathioprine : 3.3%, Mycophenolic Acid : 7.5%, Mycophenolate Mofetyl (MMF) : 71%) and 7.5% with m-TOR inhibitors. PTD prevalence was 22.7 %. The tubular proteinuria and the fractional excretion of uric acid were significantly associated with PTD (p < 0.0001). The prevalence of PTD increased with donor age (OR = 1.4, 95% CI [1.1 ; 1.7]) but was independent of cold ischemia time (p = 0.9980). An eGFR [MDRD] above 30 mL/min/1,73m² was protective (OR : 0.36, 95% CI [0.144 ; 0.92]). The immunosuppressive regimens « MMF + m-TOR inhibitors » and « MMF + Tac » were more frequently associated with PTD than « MMF + CsA » (OR = 6.4, 95% CI [1.8 ; 23.0] and OR = 3.0, 95% CI [1.3 ; 6.8], respectively). Conclusions: In renal transplant patients, after the first year post-transplantation, about one quarter of the recipients are affected by PTD, which seems partly related to the immunosuppressive regimen. Since proximal tubular cells lesions could progressively lead to tubular atrophy and interstitial fibrosis, PTD early detection and treatment may help to increase graft survival.

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