Point-of-care ultrasound (PoCUS) is commonly utilized in the setting of renal colic. The presence of perinephric fluid may be an overlooked finding associated with ureteral obstruction. Our aims were to determine the prevalence of perinephric fluid on emergency physician-performed PoCUS and to determine whether perinephric fluid was associated with stone size or urologic intervention.

This was a 12-month cross-sectional study at an academic emergency department (ED) that took place from January 1, 2022, to December 31, 2022. All adult ED patients ≥18 years of age who had a renal PoCUS examination performed were included. Patients with missing or inadequate PoCUS images were excluded. Investigators blinded to PoCUS images and interpretations performed chart review for demographic data and outcome variables, while separate investigators blinded to clinical data reviewed PoCUS images to assess for perinephric fluid and hydronephrosis. A chi-square analysis was used to determine significance of association between perinephric fluid and outcome variables (stone size, urologic intervention).

There were 442 patients screened; 18 were excluded due to inadequate images and 4 were repeat visits of which only the initial visit was analyzed. Of the remaining 420 patients included, the prevalence of perinephric fluid was 6.2% (n = 26). Most patients (23/26) with perinephric fluid had final diagnoses consistent with ureterolithiasis. Hydronephrosis was present in 115 of the 420 patients (27.4%) and of these, 22 (19.1%) had perinephric fluid which was significantly associated with a need for urologic intervention; odds ratio (OR) 10.38 (95% CI 2.70–39.85), p < 0.01. Among the 67 patients with confirmed ureterolithiasis on computed tomography, perinephric fluid was associated with stone size ≥5 mm; OR 4.00 (95% CI 1.01–15.85), p = 0.04.

The prevalence of perinephric fluid on emergency physician-performed renal PoCUS was 6.2% of all studies and 19.1% of patients with hydronephrosis. In the setting of ureterolithiasis, perinephric fluid was associated with larger stone size and need for urologic intervention.