Yes, kidney stones are highly visible on regular CT scans without contrast
Non-contrast CT is actually the gold standard imaging modality for detecting kidney stones, with a sensitivity of up to 97% and specificity of 95%, and is superior to contrast-enhanced CT for this purpose. 1, 2
Why Non-Contrast CT is Optimal for Stone Detection
- Virtually all renal calculi are radiopaque on CT, allowing accurate detection of even small stones (as small as 1 mm) without any need for IV contrast 1, 3
- The American College of Radiology specifically recommends non-contrast CT as the reference standard for evaluating urolithiasis 1, 2
- Non-contrast CT directly visualizes calculi throughout the entire ureter from the kidney to the bladder, independent of any urinary tract opacification 2
Contrast CT Actually Performs Worse for Stone Detection
- Contrast-enhanced CT has lower sensitivity (81% overall, 95% for stones ≥3 mm) compared to non-contrast CT's 97% sensitivity 3
- The only exception is that stones ≥6 mm can still be detected with approximately 98% accuracy on contrast studies if that's what was already performed 3
- There is no documented additional benefit of adding contrast to non-contrast CT for stone evaluation 1
Technical Capabilities of Non-Contrast CT
- Detects stones throughout their entire path: kidney, ureter, and bladder 2
- Provides accurate stone size measurements (critical for treatment planning) using coronal reformations, bone window settings, and magnified views 1, 3
- Shows secondary signs of obstruction including hydronephrosis, periureteral inflammation, and ureteral dilation 1
- Low-dose protocols (<3 mSv) maintain the same 97% sensitivity while reducing radiation exposure 1, 3
Rare Exceptions
- Only extremely rare radiolucent stones (such as certain pure uric acid stones) might be missed, but these represent <5% of all stones 4
- Very small stones (<3 mm) may occasionally be missed, particularly with aggressive dose reduction protocols 1
- One case report documented a large calcium oxalate stone missed on CT, but this is extraordinarily rare 4
Common Pitfall to Avoid
Do not request contrast CT specifically for stone detection—it adds unnecessary cost, radiation exposure, contrast-related risks, and actually reduces sensitivity for small stones compared to non-contrast imaging 1, 3. The only scenario where contrast might be added is if you need to evaluate alternative diagnoses beyond stones (such as complex renal cysts or masses), but this should be a separate clinical decision 5.