Value of Doppler parameters in the diagnosis of renal artery stenosis.

PURPOSE: Our purpose was to assess the accuracy and optimal threshold values of the Doppler parameters of the renal arteries and parenchyma for detecting renal artery stenosis (RAS) greater than 60% and occlusion.

METHODS: Renal duplex ultrasonography and standard angiographic studies of the renal arteries were performed in 78 patients for comparative analysis. Three degrees of RAS were considered: less than 60%, greater than 60%, and occlusion. The following parameters of the Doppler wave were measured in the signal obtained from the main renal artery and interlobar arteries: peak systolic velocity (PSV), end-diastolic velocity, peripheral resistance index, acceleration time, acceleration index, and renal/aortic ratio (RAR).

RESULTS: Logistic regression analysis identified the PSV in the renal artery as the best parameter to differentiate RAS less than 60% from RAS greater than 60%. Only when this parameter was excluded were the RAR and end-diastolic velocity in the renal artery the variables accepted as the best predictors. Receiver-operator curve analysis revealed a PSV in the main renal artery greater than 198 cm/sec and RAR greater than 3.3 as the best cutoff points for detecting RAS greater than 60%. A PSV above this threshold provided 87.3% sensitivity and 91.5% specificity. The RAR showed similar specificity (92.4% but a much lower sensitivity (76.4%). A kidney length less than 8.5 cm, in addition to an absent Doppler signal in renal parenchyma, was the best criterion to identify renal artery occlusion. On the basis of the above-mentioned criteria, renal duplex scanning correctly identified 86 of 94 cases of RAS less than 60%, 41 of 48 cases of RAS greater than 60%, and six of seven occlusions (kappa value = 0.8).

CONCLUSION: These results suggest that the PSV in the renal artery is the best predicting Doppler parameter to detect RAS greater than 60%. A PSV greater than 198 cm/sec may be an appropriate cutoff point to diagnose this group of stenosis. The RAR did not add any predicting utility in this series. An absent Doppler signal in the renal parenchyma and a kidney length less than 8.5 cm were the best predictors of renal artery occlusion.