Diagnostic Imaging for Suspected Kidney Stones

Primary Recommendations

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% 1
Non-contrast CT detects virtually all renal calculi regardless of composition, providing accurate detection even of small stones without requiring IV contrast 1
CT provides precise stone size measurement and exact anatomical location within the ureter, which is crucial for determining whether observation versus intervention is appropriate 1
CT identifies secondary signs of obstruction including periureteral inflammation, perinephric inflammation, and ureteral dilatation that help confirm clinical significance 1

Ultrasound alone has poor sensitivity (24-57%) for stone detection, making it inadequate as a standalone test 1
Adding plain radiography (KUB) to ultrasound improves diagnostic accuracy to 79-90% sensitivity, though this remains inferior to CT 1, 2
Use ultrasound as first-line only in pregnant patients where radiation must be avoided 1, 2

In patients where CT is inconclusive or unavailable, MRI with noncontrast MR urography can detect upper tract obstruction using secondary signs with 84% sensitivity, 100% specificity, and 86% accuracy when radiation must be avoided and ultrasound is inconclusive 1
For recurrent stone formers, limit CT scans to the area of interest or use ultra-low-dose protocols to reduce cumulative radiation exposure 1
Consider alternating with ultrasound for routine surveillance when clinical suspicion is low 1

Serum creatinine should be assessed to evaluate renal function, particularly if obstruction is suspected 3