Clinical Use and Value of Renal Ultrasonography for Suspected Urolithiasis in the Emergency Department

Abstract

Purpose: Computed tomography (CT) has the highest sensitivity and specificity for urolithiasis in patients with acute flank pain. However, some studies have suggested that ultrasound (US) should be the initial imaging test in the Emergency Department (ED) for suspected urolithiasis. The purpose of this study is to assess the value of renal US findings in predicting follow-up imaging for patients with suspected urolithiasis and, in those patients undergoing subsequent CT, the associated increases in ED length of stay (LOS) attributable to obtaining both exams. Methods: This was an IRB-approved, HIPAA-compliant retrospective study of all patients that underwent renal US in the ED from March 2018-March 2019 for acute flank pain. Data points collected were: presence of calculi and/or hydronephrosis on US, whether patients underwent follow-up imaging within 24 hours of US, presence of calculi and/or hydronephrosis on follow-up imaging, acute extra-renal findings, need for intervention, and history of urolithiasis. The time interval between placement of the US and follow-up CT orders was recorded as a surrogate for the increase in ED LOS attributable to the second test. Results: 271 patients underwent renal US in the ED for acute flank pain. 74 of 271 patients (27%) underwent follow-up imaging within 24 hours, 72 by CT abdomen/pelvis and 2 by magnetic resonance urogram (MR). Of the initial 271 US, 90 (33%) were positive for obstructive uropathy on US (demonstrating hydronephrosis or a ureteral stone). Of the 74 patients who underwent follow-up CT or MR, 32 (43%) followed a positive US and 42 (57%) followed a negative US. Of the 74 that underwent follow-up imaging, 10 had acute extra-renal findings, and 17 had subsequent intervention. The mean time interval between US and CT orders was 170 min (151 min after negative US, 197 min after positive US). Conclusions: Few cases of suspected urolithiasis underwent follow-up imaging. Of these, 43% had a positive US and 57% had a negative US, implying a large role of clinical judgement in determining the need for follow-up imaging. There is a potential to save a mean 170 min of ED LOS if imaging decisions can be made that support a single imaging exam rather than requiring subsequent CT following initial US.