Diagnostic Approach for Suspected Kidney Stones

Initial Diagnostic Approach

The American College of Radiology recommends non-contrast CT of the abdomen and pelvis as the gold standard for initial evaluation of suspected kidney stones, with sensitivity up to 97% for detecting urolithiasis and other causes of flank pain 1
Non-contrast CT of the abdomen and pelvis provides precise information about stone size, location, and density, and is particularly useful when moderate to severe hydronephrosis is present on ultrasound, as these patients have higher risk of stone passage failure 1, 2
Ultrasound is recommended as an alternative first-line option to limit radiation exposure, especially in younger patients and pregnant women, with high sensitivity for detecting large stones (>5mm), but accuracy decreases significantly for stones <3mm 1, 3
Any degree of hydronephrosis on ultrasound makes the presence of a ureteral stone on subsequent CT more likely (PPV 88%) 2, 4

For typical renal colic symptoms, non-contrast CT abdomen and pelvis is preferred first-line imaging, with consideration of low-dose CT protocols (<3 mSv) which maintain high diagnostic accuracy (sensitivity 97%, specificity 95%) 1, 2, 3
Combined ultrasound and KUB X-ray is an alternative approach, improving sensitivity for urolithiasis compared to either modality alone, and reducing radiation exposure 3, 5

Contrast-enhanced CT may obscure stones within the renal collecting system, and delayed development of secondary signs of obstruction may lead to false-negative ultrasound findings 1
Lack of hydronephrosis does not rule out kidney stones (NPV 65%) 2, 4

Repeat imaging is indicated when symptoms change or if stone passage is suspected but needs confirmation, and if medical expulsive therapy is not successful after 4-6 weeks, imaging should be performed before offering definitive treatment 3