title: Prognostic impact of renal arterial resistance index upon renal allograft survival: the time point matters.
abstract: BACKGROUND
  The renal arterial resistance index (RI) is reported to be a significant predictive parameter for renal allograft failure or death. The influence of the time point after renal transplantation on its predictive power has not been sufficiently evaluated. We performed a retrospective analysis of RI and its power to predict renal allograft failure or death with special emphasis on the time point of RI measurement.
  
  
  METHODS
  The present analysis is based on ultrasonographically recorded intrarenal arterial RI measurements, routinely obtained in our outpatient department, over a period of 13 years. Altogether, 88 patients with an RI measurement 0-3, 3-6 and 12-18 months after transplantation were included and retrospectively stratified into two groups according to the RI: those with an index >0.75 and those with an index of ≤0.75.
  
  
  RESULTS
  Twenty patients (23%) reached the combined end point, i.e. allograft failure with a return to dialysis or death. The RI measured early after transplantation (0-3 and 3-6 months) did not predict the end point, whereas the RI obtained between 12 and 18 months showed a significant predictive value for renal transplant failure or death in a univariate approach [Wald test, P = 0.0013, hazard ratio (HR) 4.787, 95% confidence interval (CI) 1.846-12.411]. At 12-18 months after transplantation, 14% (12 patients) of the study population had an RI >0.75. Seven (58%) of these patients reached the end point versus 13 of 76 patients (17%) with an RI ≤0.75. In a multivariate Cox model, the RI measured between 12 and 18 months after transplantation exhibited the highest hazard ratio (HR 6.191, 95% CI 2.288-16.756, P = 0.0003) for transplant failure or death.
  
  
  CONCLUSIONS
  In our hands, the RI obtained during the first 6 months after transplantation failed to predict renal allograft failure or death, whereas the RI measured 12-18 months after transplantation appeared useful to predict long-term allograft outcomes.
authors.affiliation: Department of Nephrology and Clinical Immunology, RWTH Aachen University, Aachen, Germany. rkramann@gmx.net
authors.forename: Rafael
authors.initials: R
authors.lastname: Kramann
authors.forename: Dario
authors.initials: D
authors.lastname: Frank
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Brandenburg
authors.forename: Nicole
authors.initials: N
authors.lastname: Heussen
authors.forename: Julia
authors.initials: J
authors.lastname: Takahama
authors.forename: Thilo
authors.initials: T
authors.lastname: Krüger
authors.forename: Jochen
authors.initials: J
authors.lastname: Riehl
authors.forename: Jürgen
authors.initials: J
authors.lastname: Floege
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D005260:Female; D006085:Graft Survival / Q000502:physiology; D006801:Humans; D016030:Kidney Transplantation / Q000000981:diagnostic imaging / Q000401:mortality / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D012077:Renal Artery / Q000000981:diagnostic imaging / Q000503:physiopathology*; D012189:Retrospective Studies; D012307:Risk Factors; D013997:Time Factors; D014463:Ultrasonography; D014655:Vascular Resistance / Q000502:physiology*; D055815:Young Adult