title: Doppler ultrasound for detection of renal transplant artery stenosis-threshold peak systolic velocity needs to be higher in a low-risk or surveillance population.
abstract: OBJECTIVE
  To establish the ideal threshold arterial velocity for the diagnosis of renal transplant artery stenosis in a surveillance population with a low pre-test probability of stenosis.
  
  
  METHODS
  Retrospective review of Doppler ultrasound, angiographic and clinical outcome data of patients transplanted over a 3-year period. Data used to calculate sensitivity, specificity, positive predictive values (PPV) and negative predictive values (NPV) for various threshold peak systolic velocity values.
  
  
  RESULTS
  Of 144 patients transplanted, full data were available in 117 cases. Five cases had renal transplant artery stenosis-incidence 4.2% [stenosis identified at a mean of 6.5 months (range 2-10 months)]. All five cases had a significant arterial pressure gradient across the narrowing and underwent angioplasty. Threshold peak systolic velocity of > or =2.5 m/s is not ideal [specificity=79% (CI 65-82%), PPV=18% (CI 6-32%), NPV=100% (CI 94-100%)], subjecting many patients to unnecessary angiography-8/117 (6%) in our population. Comparable values if the threshold is set at > or =3.0 m/s are 93% (CI 77-96%), 33% (CI 7-44%) and 99% (CI 93-100%), respectively. The clinical outcome of all patients was satisfactory, with no unexplained graft failures or loss.
  
  
  CONCLUSIONS
  In a surveillance population with a low pre-test probability of stenosis, absolute renal artery velocity > or =2.5 m/s is a limited surrogate marker for significant renal artery stenosis. The false-positive rate is high, and > or =3.0 m/s is a better choice which will halve the number of patients enduring unnecessary angiography. Close clinical follow-up of patients in the 2.5-3.0 m/s range, with repeat Doppler ultrasound if necessary, will identify the test false-negatives.
authors.affiliation: Department of Radiology, St George's Hospital, Blackshaw Road, London, UK. uday.patel@stgeorges.nhs.uk
authors.forename: U
authors.initials: U
authors.lastname: Patel
authors.forename: K K
authors.initials: KK
authors.lastname: Khaw
authors.forename: N C
authors.initials: NC
authors.lastname: Hughes
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001783:Blood Flow Velocity; D005260:Female; D006083:Graft Occlusion, Vascular / Q000000981:diagnostic imaging* / Q000503:physiopathology; D006801:Humans; D016030:Kidney Transplantation; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012078:Renal Artery Obstruction / Q000000981:diagnostic imaging* / Q000503:physiopathology; D012189:Retrospective Studies; D018608:Ultrasonography, Doppler / Q000592:standards