title: Ultrasound renal resistive index is not an organ-specific predictor of allograft outcome.
abstract: BACKGROUND
  Ultrasound-measured renal resistive index (RRI) has been suggested to predict allograft survival in renal transplant recipients. Based on experimental and clinical data, we objected to the theory that RRI specifically mirrors allograft characteristics. Instead, we hypothesized that RRI rather represents a marker of systemic vascular damage than an organ-specific marker. In order to refute this hypothesis, RRI should override the resistive index measured in other abdominal parenchymatous organs-such as the spleen-as predictor of allograft outcome. We therefore set out to simultaneously measure renal and splenic ultrasound resistive index in kidney allograft recipients.
  
  
  METHODS
  Eighty-seven stable transplant recipients were recruited. We measured RRI, splenic resistive index (SRI) and an established marker of systemic vascular damage, namely common carotid intima-media thickness (IMT). During a follow-up of 4.9 ± 0.5 years, the occurrence of the combined primary end point, defined as a decrease of ≥ 50% in estimated glomerular filtration rate (eGFR), need for dialysis treatment or death, was recorded.
  
  
  RESULTS
  At baseline, both RRI and SRI correlated with common carotid IMT [RRI: r = 0.203 (P = 0.006); SRI: r = 0.315 (P < 0.001)], but not with allograft-specific markers such as eGFR or proteinuria. Elevated RRI was a weak non-significant predictor of the combined primary end point. Notably, RRI did not surpass SRI as outcome predictor. When analysing individual components of the combined primary end point separately, elevated RRI failed to predict strictly renal events (decrease of ≥ 50% in eGFR/need for dialysis treatment), while it predicted total mortality.
  
  
  CONCLUSIONS
  Our findings support the notion that RRI is not a specific indicator of allograft damage. Similar to SRI, RRI is rather associated with systemic vascular damage markers and mortality.
authors.affiliation: Department of Internal Medicine IV, Saarland University Hospital, Homburg, Germany.
authors.forename: Sarah
authors.initials: S
authors.lastname: Seiler
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Colbus
authors.forename: Gaetano
authors.initials: G
authors.lastname: Lucisano
authors.forename: Kyrill S
authors.initials: KS
authors.lastname: Rogacev
authors.forename: Markus K
authors.initials: MK
authors.lastname: Gerhart
authors.forename: Matthias
authors.initials: M
authors.lastname: Ziegler
authors.forename: Danilo
authors.initials: D
authors.lastname: Fliser
authors.forename: Gunnar H
authors.initials: GH
authors.lastname: Heine
mesh_terms: D000328:Adult; D000368:Aged; D018572:Disease-Free Survival; D005260:Female; D006801:Humans; D007668:Kidney / Q000098:blood supply / Q000000981:diagnostic imaging*; D016030:Kidney Transplantation / Q000009:adverse effects; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D013154:Spleen / Q000098:blood supply / Q000000981:diagnostic imaging; D023001:Transplantation Tolerance / Q000502:physiology*; D014184:Transplantation, Homologous; D016896:Treatment Outcome; D014463:Ultrasonography; D014655:Vascular Resistance