Assessment of ultrasound criteria for high-grade renal artery stenosis in transplant kidneys

<h2>ABSTRACT</h2><h3>Introduction</h3> Renal artery stenosis is an uncommon vascular complication following kidney transplantation. Non-invasive renal artery duplex is frequently used for initial screening. However, due to lack of specific criteria for transplanted renal artery, renal artery stenosis is not accurately diagnosed and may result in unnecessary contrast usage for further radiographic evaluation. Given the lack of consensus on duplex criterion, as well as the risks associated with invasive angiography and contrast-enhanced CT angiography, our goal is to identify an accurate ultrasound diagnostic criteria for high grade stenosis in transplanted renal arteries. <h3>Methods</h3> A retrospective review was performed of kidney transplant patients managed with duplex screening followed by angiography. Patients underwent renal artery duplex ultrasound on the outpatient basis if there was decline in renal function or uncontrolled hypertension. Upon finding significant stenosis, patients were referred to vascular surgery for intervention. Patients who met > 60% stenosis based on the established renal artery duplex criteria were included in the study. Subjects with <i>≥</i>70% angiographic cross-sectional narrowing or mean pullback pressure gradients of <i>≥</i>10% underwent intervention. Duplex-derived peak systolic velocities measured along the donor renal artery to iliac artery were correlated with angiographic findings through receiver operating characteristic analysis. Similar calculations were performed for renal-to-iliac artery peak systolic ratios. Student's t-test and x² analysis were also evaluated. <h3>Results</h3> Forty-two patients were evaluated and were deemed to have >60% renal artery stenosis based on the established criteria and underwent angiography. Twenty one of these surgical patients were transplanted renal patients; however, four did not have angiogram data available. Thus, seventeen of those transplant patients who underwent renal angiography between January 2019 and March 2023 were reviewed. Overall mean peak velocity and mean renal-to-iliac peak systolic ratio for the 9 subjects treated with balloon angioplasty were 426 ± 34 cm/s and 2.2 ± 0.4, respectively. The 8 subjects without angiographic evidence of high-grade stenosis had an overall mean peak velocity of 271 ± 15 cm/s and mean peak ratio of 1.5 ± 0.1. There was a difference in mean peak velocity of the donor renal artery (p=0.0049) and overall mean peak velocity across the entire anastomosis (p=0.0012). For angiographic stenosis <i>≥</i>70%, an overall peak velocity of >321 correlated to 88.9% sensitivity, 100% specificity, 100% positive predictive value, and 88.9% negative predictive value with an accuracy of 94.1%. A renal-to-iliac artery peak systolic ratio <i>≥</i>1.6 corresponded to 85.7% sensitivity, 75.0% specificity, 79.4% positive predictive value, and 82.4% negative predictive value with an accuracy of 80%. Receiver operating curve analysis revealed that overall peak velocity offered the greatest discriminative power (p=0.0008) for detecting <i>≥</i>70% angiographic stenosis. <h3>Conclusions</h3> Stenosis in transplanted renal artery can lead to transplant failure and allograft loss. However, there is widespread variation on duplex diagnostic criterion, and this study underscores parameters of peak velocity >321 cm/s and ratio of peak renal-to-iliac artery velocities <i>≥</i>1.6 for predicting <i>≥</i>70% angiographic stenosis.