title: Absence of C4d urinary excretion in the early post-transplant period is associated with improved long-term kidney graft survival.
abstract: BACKGROUND
  C4d urinary excretion varies according to the risk of graft rejection or progression of chronic allograft nephropathy, but its influence on long-term kidney transplant (KTx) outcomes remains unclear. The aim of the study was to determine whether the initial (1-3 months post KTx) level of C4d urinary excretion may help to predict long-term kidney allograft transplantation outcomes.
  
  
  METHODS
  The study involved 185 patients who had undergone KTx. The urinary specimens taken from the morning urine portion were assessed by ELISA test for C4d excretion. To increase the objectivity of the assessment, all measurements were divided by urinary creatinine excretion (ng/mgCr). The study population was grouped according to the C4d excretion cut-off value into low (LC4d, 109 participants) and high (HC4d, 76 participants) C4d excretion groups. Additionally a subgroup with absence of C4d in the urine (ZC4d, 26 patients) was formed.
  
  
  RESULTS
  The calculated Roc curve indicated the cut off value of the urinary C4d excretion as 12.4ng/mgCr (AUC 0.77; 95%CI 0.73-0.95). The mean C4d urinary excretions in LC4d and HC4d were 1.9±3.27 and 20.6±4.6ng/mgCr, respectively, whereas after exclusion of ZC4d subgroup, the mean C4d was 14.9±6.3ng/mgCr in the remainder. Kaplan-Meier curve analysis demonstrated a slightly higher graft survival rate (GSR) in LC4d than in HC4d group (p=0.04 by log-rank). The subsequent analysis showed the highest GSR in ZC4d subgroup (p=0.0006 by log-rank).
  
  
  CONCLUSIONS
  Although lower C4d urinary excretion in the early post-transplant period seems to be associated with better long-term kidney allograft transplantation outcomes, only its absence in the urine appears to be a solid predictor of improved graft survival.
authors.affiliation: Department of Kidney Transplantation, Medical University of Lodz, Poland; Dialysis Department, Norbert Barlicki Memorial Teaching Hospital No. 1, 90-153 Lodz, Kopcinskiego 22, Poland. Electronic address: rzwiech@mp.pl.
authors.forename: Rafał
authors.initials: R
authors.lastname: Zwiech
mesh_terms: D000328:Adult; D064591:Allografts / Q000276:immunology; D015415:Biomarkers / Q000652:urine*; D003181:Complement C4 / Q000652:urine*; D005260:Female; D005500:Follow-Up Studies; D006084:Graft Rejection / Q000175:diagnosis* / Q000276:immunology; D006085:Graft Survival / Q000276:immunology; D006801:Humans; D016030:Kidney Transplantation; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D011446:Prospective Studies; D013997:Time Factors
chemical_list: D015415:Biomarkers; D003181:Complement C4
keywords: C4d; Kidney transplantation; Outcome; Urinary excretion