Written by Chris Thom
Spoon Feed
In patients with renal colic, absence of hematuria and hydronephrosis on point-of-care ultrasound effectively rules out obstructing kidney stones.
U-POCUS those kidneys!
The U-POCUS protocol was a retrospective study that enrolled adult patients from three emergency departments. Patients who presented with suspected renal colic and received CT imaging, point-of-care renal US, and a urinalysis were included. The definition of hematuria utilized was >2 RBCs per high-powered field or any positive blood on the dipstick if no microscopy was performed.
183 patients met inclusion criteria; 122 had ureterolithiasis, 61 did not. The sensitivity and specificity of hematuria for the presence of ureterolithiasis was 90.2% and 26.2%, respectively. The sensitivity and specificity of hydronephrosis for the presence of ureterolithiasis was 74.6% and 62.3%, respectively. The combination of hematuria and/or hydronephrosis on POCUS had a sensitivity of 99.2% (95%CI 95.6-100) for the presence of ureterolithiasis, negative predictive value 90% (95%CI 53.9–98.6).
How will this change my practice?
We can effectively rule out obstructing stone without CT. Roughly 20% of obstructing kidney stones will not produce hydronephrosis on POCUS, which makes it uncertain whether our patient still has a kidney stone even in the absence of hydronephrosis. This study adds to the literature saying that combined lack of hydronephrosis and hematuria effectively rules out an obstructing kidney stone.
POCUS pro-tips and clips
One of my favorite tips for high-quality kidney images centers around slight probe rotation when imaging the long axis view. Your indicator dot will be oriented towards the axilla. If you rotate slightly counterclockwise when imaging the right kidney and slightly clockwise while imaging the left kidney, the ultrasound beam will be directed within an intercostal space, avoiding overlying rib shadows. The biggest struggle is distinguishing normal versus mild hydronephrosis. Color doppler (to distinguish renal vasculature from hydronephrosis) and assessment of symmetry with the contralateral kidney are helpful ways to detect mild hydronephrosis.
Source
The U-POCUS protocol: urinalysis and point-of-care ultrasound to exclude symptomatic ureterolithiasis in emergency department patients. CJEM. 2025 Sep 13. doi: 10.1007/s43678-025-00998-z. Epub ahead of print. PMID: 40946134.
