Utility of Renal Point-of-Care Ultrasound for Detecting Nephrolithiasis in Emergency Department Patients With Pyelonephritis

Over one million patients are diagnosed with pyelonephritis in the emergency department (ED) each year, some of whom have concurrent nephrolithiasis, commonly referred to as a septic stone. Hydronephrosis on renal point of care ultrasound (POCUS) can help identify nephrolithiasis. Our study aims were to determine the test characteristics of POCUS for identifying nephrolithiasis in patients with pyelonephritis, along with comparing patient length of stay (LOS) for those receiving POCUS alone versus POCUS and computed tomography (CT).

A retrospective chart review of patients in a tertiary hospital ED from 1/1/2015 to 4/30/2025 was conducted. Patients were included if they were diagnosed with pyelonephritis based on ICD-10 code and received a renal POCUS at the index visit. Chart review was performed by blinded chart abstractors to collect patient demographics, imaging results, timing, LOS, disposition, urological procedure history, and ED return visits within 14 days. POCUS image review was conducted in QPathE by two blinded ultrasound fellows for the presence of hydronephrosis. Statistics were performed using SPSS, using alpha < 0.05 for significance.

A total of 440 patients were reviewed, 87 of which were excluded. There were 190 patients who had both renal POCUS and CT, and 163 patients who had renal POCUS alone. Twenty-two patients had concurrent nephrolithiasis (6.2%), with only three (0.85%) lacking hydronephrosis on renal POCUS. POCUS alone had a sensitivity of 100% and a specificity of 92.3% (CI 87% to 96%) for identifying nephrolithiasis, producing a negative predictive value of 98.8% (CI 96.7% to 99.6%). POCUS and CT had a similar negative predictive value of 98.1% (CI 95% to 99.3%). None of the patients with no hydronephrosis on POCUS required urological procedural intervention or returned within 14 days with nephrolithiasis. A total of 193 patients were discharged; the total length of stay for POCUS alone was 263.9 min (SD 131.9 min) versus 363.8 min (SD 168.5 min) for POCUS plus CT (p < 0.001).

Our study found that renal POCUS was an accurate and fast screening tool in patients with pyelonephritis in the ED for concurrent nephrolithiasis, reducing overall ED length of stay and radiation exposure for patients without missing cases of septic stone.