What are the indications, preparation steps, and contraindications for a CT urogram?

CT Urogram Overview

CT urography (CTU) is the first-line imaging modality for evaluating the urinary tract, particularly indicated for gross hematuria and high-risk patients with microhematuria, having superseded traditional excretory urography 1, 2.

Primary Indications

Strong Indications (First-Line Imaging)

• Gross hematuria - carries 30-40% malignancy risk and mandates full urologic workup 1
• High-risk microhematuria with any of these factors 1:
  • Age >35 years
  • Male gender
  • Smoking history
  • Occupational chemical exposure
  • History of pelvic irradiation
  • Chronic urinary tract infection
  • Analgesic abuse
  • Irritative voiding symptoms
  • Exposure to carcinogenic agents or chemotherapy

Secondary Indications

• Staging of bladder cancer 2
• Evaluation of unclear kidney or ureteral findings 2
• Problem-solving examination when other modalities are inconclusive 3

When NOT to Image

Do not perform CTU in patients with microhematuria and identified benign causes including 1:

• Vigorous exercise
• Active infection (confirm with urine culture first)
• Recent trauma
• Menstruation
• Recent urologic procedure

These patients derive no benefit from imaging. Anticoagulant therapy does NOT alter the need for evaluation if hematuria is present 1.

Technical Protocol

Standard CTU Components 1, 3

CTU is specifically tailored for urinary tract visualization and requires:

1. Unenhanced phase (optional, low-dose CTDIvol 2-3 mGy)
2. IV contrast administration
3. Nephrographic phase
4. Excretory phase (acquired ≥5 minutes post-contrast)
5. Thin-slice acquisition with multiplanar reconstruction

Protocol Options 3

Split-Bolus Technique:

• Initial loading dose of IV contrast
• Second dose followed by combined nephrographic-excretory phase acquisition
• More efficient, reduces phases

Single-Bolus Technique:

• Separate nephrographic and excretory phases
• More traditional approach

Radiation Dose Stratification 3

• Low dose (CTDIvol 5-6 mGy): Benign conditions
• Normal dose (CTDIvol 9-12 mGy): Suspected malignancy
• Unenhanced series (CTDIvol 2-3 mGy): When needed

Contraindications

Absolute Contraindications

• Severe contrast allergy (anaphylaxis to iodinated contrast)
• Severe renal impairment (use MR urography instead) 2, 4

Relative Contraindications

• Pregnancy - MR urography is preferred alternative 4
• Children - MR urography preferred to avoid radiation 4
• Moderate renal dysfunction - requires risk-benefit assessment

Alternative: MR Urography

When CT is contraindicated, MR urography serves as a feasible alternative 2. MRU protocol includes 1:

• Heavily T2-weighted imaging (unenhanced)
• IV gadolinium contrast with corticomedullary, nephrographic, and excretory phases
• Thin-slice multiplanar imaging

Critical Distinction

Standard "CT abdomen/pelvis with contrast" is NOT equivalent to CT urography 1. CTU specifically requires both precontrast and excretory phases with thin-slice acquisition optimized for urinary tract evaluation. Using a non-tailored protocol will miss urothelial pathology.

Preparation Steps

1. Patient hydration - IV hydration before examination 5
2. Timing optimization - ensure adequate contrast bolus timing 5
3. Bladder management - maximize urinary tract distension and opacification 5
4. Diuretics - may be administered to improve excretory phase 6

Clinical Pitfall

The most common error is ordering "CT abdomen/pelvis with contrast" when CTU is actually needed for hematuria evaluation. This misses the critical excretory phase and precontrast imaging necessary for detecting urothelial malignancies 1.