Microscopic Hematuria: CT Urography vs Ultrasound
CT urography (CTU) is the imaging study of choice for evaluating microscopic hematuria in patients with risk factors, demonstrating 96% sensitivity and 99% specificity for detecting urothelial malignancy. 1
Risk Stratification Determines Imaging Choice
The appropriate imaging modality depends critically on patient risk factors:
High-Risk Patients (Require CTU)
Patients with any of the following risk factors should undergo CT urography as first-line imaging: 1
- Age >50 years
- Smoking history
- Occupational exposure to chemicals or dyes
- History of gross hematuria
- History of urologic disorders or disease
- History of irritative voiding symptoms
- History of pelvic irradiation
- History of chronic UTI
- Analgesic abuse
- Exposure to known carcinogens
Low-Risk Patients (No Imaging Needed)
Ultrasound is not useful as first-line imaging for microscopic hematuria in patients without risk factors who have an identified benign cause (recent vigorous exercise, infection, viral illness, menstruation, or renal parenchymal disease). 1 In patients <40 years without risk factors, no malignancy-related findings were identified at CTU in one study of 442 patients. 1
Why CTU Outperforms Ultrasound
CTU provides superior diagnostic accuracy compared to ultrasound across all urinary tract segments: 1
- Upper tract detection: CTU achieves 99.6% accuracy for kidney and ureter lesions 1
- Lower tract detection: 98.8% specificity and 97.2% accuracy for bladder lesions 1
- Comprehensive evaluation: CTU evaluates both nephrogenic and urogenic causes in a single examination 1
In direct comparison, ultrasound demonstrated lower sensitivity for detecting urinary tract abnormalities compared to CTU. 1 However, one large prospective study found that in the low-risk microscopic hematuria population, urinary cancer occurred in only 0.4% of patients, and all cases were renal carcinomas detectable by ultrasound. 1
Special Populations Requiring Modified Approach
Impaired Renal Function (eGFR <45 mL/min)
MR urography without and with IV contrast is the most appropriate imaging when CTU is contraindicated due to impaired renal function. 2 The protocol should include heavily T2-weighted sequences, pre-contrast T1-weighted imaging, post-contrast sequences, and thin-slice acquisition with multiplanar imaging. 2
Pregnancy
Ultrasound of kidneys and bladder is the recommended first-line imaging for hematuria in pregnancy, with comprehensive workup deferred until after delivery. 3 The malignancy rate in pregnant women with hematuria is low, and radiation exposure must be avoided. 1, 3 MR urography without IV contrast may be reasonable in select cases, but gadolinium-based contrast should be avoided due to uncertain fetal effects. 1, 3
Young Patients (<40-50 years) Without Risk Factors
Non-contrast CT or ultrasound may be reasonable in patients <50 years of age with microscopic hematuria. 1 If gross hematuria develops, cystoscopy should be added. 4
Critical Technical Requirements for CTU
The CTU protocol must include three phases to maximize diagnostic yield: 1
- Unenhanced phase: Optimal for detecting renal calculi 5
- Nephrographic phase: Best for visualizing renal parenchymal abnormalities and masses 5
- Excretory phase: Essential for detecting urothelial lesions and filling defects 1, 6
Thin-slice acquisition and multiplanar imaging should be obtained. 1 The excretory phase is particularly critical—it allows the urinary collecting system to be distended with contrast, enabling detection of abnormalities that would be missed without this phase. 6
Common Pitfalls to Avoid
Do not order conventional CT abdomen/pelvis with contrast instead of CTU—this lacks the pre-contrast and excretory phases necessary for comprehensive urinary tract evaluation. 1 CTU has replaced conventional CT because of improved detection of urothelial lesions. 1
Do not use ultrasound as first-line imaging in high-risk patients—it has inferior sensitivity for detecting urinary tract abnormalities compared to CTU and MR urography. 1 Small urothelial lesions are particularly difficult to detect with ultrasound. 2
Do not order intravenous urography (IVU)—this modality is obsolete, with only 84.9% accuracy compared to 99.6% for CTU. 1
Age-Specific Diagnostic Thresholds
Patients ≥40 years with ≥5 RBCs/HPF on urinalysis warrant full evaluation with CTU and cystoscopy. 4 Age and degree of hematuria are the only significant predictors of genitourinary cancer on multivariate analysis. 4 In patients >40 years, 31 had malignancy and 32 had stones in one series, compared to only 1 malignancy and 7 stones in patients ≤40 years. 4
Patients with <5 RBCs/HPF on three urinalyses are unlikely to have significant pathology and could be followed conservatively. 4