CT Abdomen Without Contrast for Kidney Stone Detection

Diagnostic Accuracy and Guidelines

The American College of Radiology guidelines state that non-contrast CT (NCCT) is the imaging modality of choice for evaluating suspected urolithiasis, with a sensitivity of 97% for stone detection 1
The American College of Radiology recommends NCCT for suspected kidney stones, as it provides accurate detection of even small stones without IV contrast, with a specificity of 95% in pooled analyses 1
NCCT detects stones as small as 1 mm in diameter, and provides rapid acquisition with high spatial resolution and multiplanar reformation capabilities 1
The American College of Radiology guidelines suggest that NCCT accurately depicts stone size and location, which is critical for predicting spontaneous passage rates 1

Low-dose CT protocols (<3 mSv) should be standard practice to minimize radiation exposure while maintaining diagnostic accuracy, with a confirmed 97% sensitivity and 95% specificity 2
Technical optimization for accurate measurements includes using coronal reformations, bone window settings, magnified views, and thin (1-1.5 mm) axial slices 1, 2
The American College of Radiology suggests that contrast-enhanced CT has limitations, including an overall sensitivity of 81% for all stones, and a sensitivity of 95% for stones ≥3 mm, which is still inferior to NCCT 1

Ultrasound may be appropriate for pregnant patients where radiation must be avoided, but it has a lower sensitivity of 45% for renal calculi and 54% overall sensitivity 2
In emergency settings, ultrasound combined with clinical assessment may be reasonable, but definitive stone characterization requires CT 3, 4
If contrast CT has already been performed, stones ≥6 mm can still be detected with high accuracy (approximately 98%) 1