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

AIMS: 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 ≥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 ≥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 ≥2.5 m/s is a limited surrogate marker for significant renal artery stenosis. The false-positive rate is high, and ≥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.