Clinical utility of gray scale renal ultrasound in acute kidney injury

BACKGROUND: Acute kidney injury occurs commonly in hospitalized patients and is associated with significant morbidity and mortality. Although renal ultrasound is often performed, its clinical utility in determining of the cause of acute kidney injury, particularly the detection of urinary tract obstruction, is not established. METHODS: Retrospective cohort study of all adult inpatients that underwent renal ultrasound for acute kidney injury over a 3-year period at a large university teaching hospital. The frequency of renal ultrasound abnormalities and clinical characteristics that predicted the finding of urinary tract obstruction was determined. RESULTS: Over the 3-year period, 1471 renal ultrasounds were performed of which 55% (810) were for evaluation of acute kidney injury. Renal ultrasound was normal in 62% (500 of 810) of patients. Hydronephrosis was detected in only 5% (42 of 810) of studies and in only 2.3% (19 of 810) of the cases was obstructive uropathy considered the cause of acute kidney injury. The majority of these patients (14 of 19) had a medical history suggestive of urinary tract obstruction. Less than 1% of patients (5 of 810) had urinary tract obstruction on ultrasound without a suggestive medical history. Most other ultrasound findings were incidental and did not establish an etiology for the acute kidney injury. CONCLUSIONS: Renal ultrasound for evaluation of acute kidney injury is indicated if there is medical history suggestive of urinary tract obstruction. Otherwise, renal ultrasound is unlikely to yield useful results and should be used more selectively based on patients’ medical history.