Is a computed tomography (CT) stone protocol the same as a computed tomography (CT) urogram?

No, CT Stone Protocol and CT Urogram Are Distinct Examinations

A CT stone protocol (noncontrast CT) and a CT urogram (CTU) are fundamentally different examinations with different indications, techniques, and diagnostic capabilities. 1, 2

Key Technical Differences

CT Stone Protocol

• Performed without intravenous contrast to maximize stone visualization 2
• Single-phase acquisition (unenhanced only) 1
• Optimized specifically for detecting urinary tract calculi with thin-slice acquisition 2
• Typically uses low-dose technique (<3 mSv) with 97% sensitivity and 95% specificity for stone detection 1, 2
• Covers kidneys, ureters, and bladder 2

CT Urogram (CTU)

• Requires intravenous contrast with multiple phases 1
• Includes precontrast phase, nephrographic phase, and delayed excretory phase (at least 5 minutes post-contrast) 1, 3
• Specifically tailored for comprehensive evaluation of the upper and lower urinary tracts 1
• The excretory phase opacifies and distends the urinary tract for optimal urothelial visualization 1, 3
• Uses thin-slice acquisition with multiplanar reformations (maximum intensity projection or 3-D volume rendering) 1, 3

Critical Diagnostic Capability Differences

What CT Stone Protocol Can Do

• Detect virtually all renal calculi with 97% sensitivity (stones are radiopaque on CT) 1
• Accurately assess stone size and location for treatment planning 1, 2
• Visualize secondary signs of urolithiasis (periureteral inflammation, ureteral dilatation) 1
• Predict spontaneous stone passage rates based on size and location 1, 2

What CT Stone Protocol Cannot Do

• Cannot reliably detect or characterize bladder or kidney cancers because it lacks contrast enhancement needed to identify enhancing tumors 4
• Cannot distinguish enhancing tumors from nonenhancing blood clots or calculi 4
• Cannot confirm ureteral location of calculus versus phlebolith mimics 1
• Cannot adequately evaluate urothelial thickening, focal lesions, or degree of obstruction 1

What CTU Adds Beyond Stone Protocol

• Detects urothelial malignancies with 91% diagnostic accuracy, 87% sensitivity, and 99% specificity 4
• Confirms ureteral location of calculi and distinguishes from phleboliths 1
• Better confirms degree of obstruction caused by ureteral stones 1
• Comprehensive evaluation of entire urothelial surface for filling defects and masses 4
• Can detect radiolucent stones (rare entity) 1

When to Order Each Examination

Order CT Stone Protocol (Noncontrast CT) When:

• Primary concern is acute urolithiasis in patients with flank pain 2
• Evaluating stone size and location for treatment planning (spontaneous passage vs. intervention) 2
• Following known stone disease 2
• Patient has contraindication to IV contrast 1

Order CT Urogram (CTU) When:

• Evaluating hematuria (CTU is the recommended initial imaging test) 4, 5
• Suspected urothelial malignancy (bladder or upper tract) 3, 4
• Staging or surveillance of urinary tract malignancies 6
• Suspected bladder pathology including tumors, fistulas, or structural abnormalities 3
• Need to distinguish stone from phlebolith or other filling defect 1

Order Standard CT Abdomen/Pelvis With Contrast When:

• Evaluating alternative diagnoses beyond stones (abscess, malignancy, vascular pathology) 2
• Assessing complications such as infection, pyelonephritis, or renal abscess 2

Common Pitfalls to Avoid

• Do not order contrast-enhanced CT as first-line for suspected stones—it provides no advantage and may reduce sensitivity for small calculi 2
• Do not rely on incidental findings from a stone protocol CT to rule out cancer—if there is clinical suspicion for malignancy, order CTU 4
• Do not confuse "CT abdomen and pelvis without and with IV contrast" with CTU—the former lacks both the precontrast and excretory phases necessary for proper urinary tract evaluation 1
• Noncontrast CT has 97% sensitivity for urolithiasis but is the reference standard specifically for stone detection, not comprehensive urinary tract evaluation 1
• CTU may miss small or flat bladder lesions—cystoscopy remains the gold standard for direct bladder visualization 4
• Recognize that 2-4% of patients with bladder cancer have concurrent upper tract disease, requiring comprehensive evaluation with CTU 4