Does Renal Ultrasound Show Kidney Stones?
Yes, renal ultrasound can detect kidney stones, but it has significant limitations with variable sensitivity of 24-57% for direct stone detection and frequently misses smaller stones, making it inferior to CT scan for stone diagnosis. 1
Direct Stone Detection Performance
Gray-scale ultrasound demonstrates poor-to-moderate sensitivity (24-57%) for detecting kidney stones compared to CT scan, with performance heavily dependent on stone size and location 1
Ultrasound sensitivity improves to 70-93% for detecting at least one stone per kidney, though it frequently misses additional stones when multiple calculi are present 2, 3
**Stones <5 mm are particularly problematic**, with ultrasound missing 30-66% of small stones and detecting only stones >5 mm reliably 1, 3
Ultrasound tends to overestimate stone size by 1.9 mm on average for stones ≤5 mm, which can inappropriately influence management decisions 1, 4
Enhanced Detection Techniques
Adding color Doppler with twinkling artifact assessment can increase sensitivity to 99% for small renal stones (<5 mm), but this comes with a false-positive rate up to 60% 1
Combining ultrasound with KUB radiography improves sensitivity to 79-90%, though this still falls short of CT's 93-96% sensitivity 1
Indirect Signs of Stone Disease
Ultrasound excels at detecting secondary signs of obstruction (hydronephrosis, ureterectasis, perinephric fluid) with up to 100% sensitivity and 90% specificity 1
Critical caveat: These secondary signs may not develop within the first 2 hours of presentation, reducing early diagnostic utility 1
Absence of hydronephrosis on ultrasound makes a larger ureteral stone (>5 mm) less likely, providing useful negative predictive value 1
Ureteral Stone Detection
Ultrasound performs even worse for ureteral stones with sensitivity of only 45-61%, though specificity remains high at 100% when obstruction is present 1, 5
Stones in the mid and distal ureter are particularly difficult to visualize on ultrasound 5, 6
Clinical Recommendations from Guidelines
The American College of Radiology (2023) and European Association of Urology (2025) recommend ultrasound as the primary initial diagnostic tool for suspected kidney stones, but emphasize it should not delay emergency care 1, 5
Non-contrast CT should follow ultrasound when stone disease is suspected but not confirmed, as CT remains the gold standard with 93-96% sensitivity and 93-100% specificity 1, 5
For pregnant women and children, ultrasound is strongly recommended as first-line imaging to avoid radiation exposure 1
Key Pitfalls to Avoid
Do not rely on ultrasound alone to rule out kidney stones—negative ultrasound does not exclude stone disease, particularly for stones <5 mm 1, 5, 6
Dehydration may mask obstruction on ultrasound, leading to false-negative results 6
Stone location matters significantly—left upper calyx stones have particularly low detection rates on ultrasound 2
Do not use KUB radiography as a standalone test—it has only 8% sensitivity for stones <5 mm and should not replace CT when stone diagnosis is critical 1, 5