Background: Renal ultrasounds (RUS) are commonly ordered in hospitalized patients with acute kidney injury (AKI). Clinical decision support tools could be used to inform which patients may benefit from RUS to rule out hydronephrosis, however current risk stratification frameworks are underutilized.Methods: We performed a cross-sectional study of hospitalized adults with AKI at a large, tertiary, academic medical center who had a RUS ordered. We validated an existing risk stratification

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... to predict hydronephrosis based on 7 criteria. Outcomes were presence of unilateral or bilateral hydronephrosis and incidental findings on RUS. Results: Two hundred and eighty-one patients were included in the study cohort; 111 (40%), 76 (27%), and 94 (33%) patients were in the high-, medium-, and low-risk groups for hydronephrosis, respectively, based on the risk stratification framework. Thirty-five patients (12%) were found to have hydronephrosis, of whom 86% were captured in the high-risk group. A nephrology consult was involved in 168 (60%) patients and RUS was recommended by the nephrology service in 95 (57%) cases. Of the 95 patients recommended for a RUS, 9 patients (9%) had hydronephrosis. Among the patients with a nephrology consultation, 9 (56%) of the 16 total patients with hydronephrosis were recommended to obtain a RUS. Conclusions: We further validated a risk stratification framework for hydronephrosis and found that nephrology recommendations predicted hydronephrosis less well than the risk stratification framework. Decision support tools for hydronephrosis may be useful to supplement clinical judgement in the evaluation of AKI.