Imaging Recommendations for Suspected Kidney Stones

Initial Imaging Modality

The American College of Radiology recommends that non‑contrast computed tomography (CT) of the abdomen and pelvis be used as the first‑line imaging study for adults with acute flank pain and suspected urolithiasis, rather than a plain abdominal X‑ray (KUB). [1][2]

KUB detects only about 8 % of stones ≤5 mm and 78 % of stones >5 mm when CT is used as the reference standard, indicating very low sensitivity for small calculi. 1
Overall sensitivity of KUB for stones of any size or location is ≈ 29 %, improving to ≈ 72 % for large (>5 mm) proximal ureteral stones. 1
Sensitivity of KUB is limited by multiple factors, including stone composition, anatomical location, size, patient body habitus, and overlying bowel contents. 1
On a single two‑dimensional view, KUB cannot reliably differentiate phleboliths from ureteral stones, leading to potential diagnostic confusion. 1

Ultrasound shows poor sensitivity (24–57 %) for direct detection of urinary stones and up to 61 % sensitivity for ureteral stones, making it a suboptimal primary test in most adults. 1

For an adult presenting with acute flank pain and suspected urolithiasis, the recommended pathway is:

The American College of Radiology concludes that KUB has no role in the initial evaluation of suspected kidney stones in contemporary practice. [1][2]

The American College of Radiology recommends low-dose non-contrast CT of the abdomen and pelvis as the gold standard initial imaging test for suspected kidney stones, with sensitivity of 97% and specificity of 95% 3, 4
Low-dose non-contrast CT should be used as the first-line imaging modality for suspected kidney stones in most patients, providing accurate detection of even small stones without IV contrast 3, 4
Virtually all renal calculi are radiopaque on CT, allowing accurate detection of stones 3
Non-contrast CT provides precise measurement of stone size and exact location within the ureter, crucial for determining management 3
Detection of secondary signs including periureteral inflammation, perinephric inflammation, and ureteral dilatation is possible with non-contrast CT 3, 4

The American College of Radiology suggests ultrasound of kidneys and bladder as the appropriate first-line test for pregnant patients due to radiation concerns 4
Ultrasound is reasonable for pediatric patients and patients requiring frequent follow-up imaging for recurrent stone disease 4
However, ultrasound has limited sensitivity for stone detection, with sensitivity of 24-57% compared to CT 4
Adding plain radiography (KUB) to ultrasound improves diagnostic accuracy to 79-90% sensitivity 4, 5, 6, 7

MRI has limited utility for stone detection but can be considered when radiation must be avoided and ultrasound is inconclusive, with noncontrast MRU detecting upper tract obstruction with sensitivity of 84%, specificity of 100%, and accuracy of 86% using secondary signs 4, 5, 6, 7, 8, 9
For patients with recurrent stones, limit the CT scan to the area of interest or use ultra-low-dose protocols to reduce cumulative radiation exposure, but be aware that ultra-low-dose protocols may miss stones <2mm in size 3, 4