Diagnostic Testing for Suspected Kidney Stones

First-Line Diagnostic Testing

Non-contrast CT scan is the gold standard diagnostic test for suspected kidney stones, with sensitivity of 97% and specificity of 95%, and should be the first-line imaging modality when kidney stones are suspected, according to the American College of Radiology 1
Low-dose CT protocols (<3 mSv) should be used to reduce radiation exposure while maintaining excellent diagnostic performance (pooled sensitivity 97%, specificity 95%) 1
Non-contrast CT can also detect secondary signs of urolithiasis including periureteral inflammation, perinephric inflammation, and ureteral dilatation 1

Ultrasound (US) of kidneys and bladder is a reasonable alternative first-line test, particularly in pregnant patients due to radiation concerns, and in children, as recommended by the Journal of the American College of Radiology 1, 2
Ultrasound demonstrates variable performance compared to CT, with sensitivity of 24-57% for stone detection, and up to 100% sensitivity and 90% specificity for diagnosing ureteral obstruction (hydronephrosis, ureterectasis, perinephric fluid) 2
The addition of color Doppler with twinkling artifact assessment can improve sensitivity for small renal stones 3

Combining ultrasound with plain radiography (KUB) improves diagnostic accuracy, with a combined sensitivity of 79-90% for detecting stones, as reported by the Journal of the American College of Radiology 2, 3

Intravenous Urography (IVU) has lower sensitivity and specificity (87% and 94%) compared to non-contrast CT (96% and 100%), according to the Journal of the American College of Radiology 4
MRI has limited utility in stone detection but can be considered when radiation exposure must be avoided and ultrasound is inconclusive, as suggested by the Journal of the American College of Radiology 4
Plain radiography (KUB) alone has limited sensitivity (29% overall, 72% for stones >5mm in proximal ureter) 4

Relying solely on ultrasound for small stones (<5mm) as sensitivity decreases significantly, as warned by the Journal of the American College of Radiology 2
Using contrast-enhanced CT as first-line imaging, which may lead to missed small stones, according to the American College of Radiology 1
Failing to consider hydronephrosis on ultrasound as a marker for possible obstruction, even when stones are not visualized, as cautioned by the Journal of the American College of Radiology 2

For patients with recurrent stone disease, limiting the CT scan to the area of interest or using ultra-low-dose protocols helps reduce radiation exposure, as recommended by the American College of Radiology 1