Best duplex-sonographic criteria for the assessment of renal artery stenosis--correlation with intra- arterial pressure gradient.

PURPOSE: Colour coded duplex sonography (DS) is widely used for the assessment of renal artery stenosis (RAS). Different criteria have been specified for the detection of significant RAS. The aim of our study was to compare routinely used DS criteria, both with intra-arterial pressure gradients and arteriographic degree of stenosis, and to validate different cut-off points of these DS criteria for the assessment of haemodynamically significant RAS.

MATERIALS AND METHODS: We retrospectively analysed forty-nine patients (median age 67 years, 29 male) with RAS documented by duplex sonography, referred for renal arterial subtraction arteriography and intra-arterial pressure measurement (93 renal arteries). DS measurement of peak systolic velocity (PSV) in the main renal artery, the renal/aortal velocity ratio (RAR) and the side-to-side differences of the intrarenal resistive indices (DeltaRI) were correlated to intra-arterial pressure measurements and arteriographic degree of stenosis. Receiver operating characteristics (ROC) were used to determine the best cut-off value of DS criteria.

RESULTS: 39 (41 %) renal arteries had normal findings or non significant stenosis < 50 %, 23 (25 %) had a diameter reduction between 50 % and 69 %, and 31 (33 %) > or = 70 %. The systolic pressure gradient showed good correlation with the arteriographic degree of RAS (r = 0.77, p < 0.001) and the PSV measured by duplex sonography (r = 0.67, p < 0.001). Mean systolic pressure gradient was 24 mmHg at 50 % stenosis and 23 mmHg at PSV of 200 cm/sec. A PSV of > or = 200 cm/sec provided a sensitivity of 92 % and specificity of 81 % for detecting RAS of > or = 50 %. Similar results were found for RAR > or = 2.5 with a sensitivity of 92 % and specificity of 79 %. These cut-off values have a negative predictive value of 100 % for excluding high-grade RAS of > or = 70 %. A DeltaRI of > or =0.05 has low sensitivity of 31 %, but a high specificity of 97 % for detecting RAS of > or = 50 %.

CONCLUSION: DS measurements and the severity of arteriographic diameter reduction correlate well with systolic pressure gradients. Clinically expedient DS criteria for detecting RAS of > or = 50 % are a PSV of > or = 200 cm/sec or a RAR of > or =2.5. These criteria allow reliable exclusion of severe RAS of > or = 70 %.