Most Appropriate Investigation
For this patient presenting with hematuria and right flank pain, the most appropriate initial investigation is non-contrast CT of the abdomen and pelvis (CT KUB). 1, 2
Clinical Reasoning
This patient's presentation—red urine (hemoglobinuria), right flank pain, absence of fever, and no trauma history—strongly suggests urolithiasis as the primary differential diagnosis. The palpable prostate is likely an incidental finding in an adult male and does not alter the initial diagnostic approach for acute flank pain with hematuria.
Why Non-Contrast CT is the Gold Standard
Non-contrast CT has superior diagnostic accuracy with sensitivity and specificity both exceeding 90% for detecting urinary tract stones, making it the definitive imaging modality for suspected urolithiasis 1, 2, 3
The American College of Radiology recommends non-contrast CT KUB for initial evaluation of suspected urolithiasis due to its ability to detect nearly all types of urinary calculi regardless of composition 2, 4
CT provides comprehensive evaluation beyond stone detection, including assessment of stone burden, degree of hydronephrosis, and identification of alternative diagnoses such as renal masses, UPJ obstruction, or other anatomic abnormalities 2, 5
Critical Clinical Considerations
The absence of hematuria does not exclude urolithiasis—approximately 7% of patients with renal colic may have negative urine dipstick testing, so the presence of hematuria in this case strongly supports but is not required for the diagnosis 2
Ultrasound has significant limitations in this clinical scenario, detecting only 75% of all urinary tract stones and merely 38% of ureteral stones, making it inadequate as the sole initial imaging modality 2
Plain radiography (KUB) is not appropriate for initial evaluation, with inadequate sensitivity of only 59% for stone detection and no information about obstruction degree or soft tissue pathology 2
Alternative Diagnoses to Consider
While urolithiasis is most likely, non-contrast CT will also evaluate for:
- Renal masses or tumors that can present with hematuria and flank pain 2
- Page kidney (subcapsular hematoma causing secondary hypertension), which can mimic nephrolithiasis 6
- UPJ obstruction causing similar symptoms 2
When to Consider CT Urography Instead
If the non-contrast CT is negative but hematuria persists, particularly in a patient with risk factors (male gender, age >35 years, smoking history), CT urography (CTU) with IV contrast should be performed to evaluate for urothelial malignancy, as bladder cancer is the most common malignancy detected in patients with hematuria 1, 3
Management Algorithm Based on CT Findings
If stones are identified: Management depends on size, location, and degree of obstruction—stones >4mm or those causing significant obstruction may require urologic intervention 7
If moderate to severe hydronephrosis is present: These patients are at higher risk of stone passage failure and may require more aggressive management 8
If CT is negative: Consider cystoscopy and contrast-enhanced imaging (CTU or MRU) to evaluate for urothelial malignancy, particularly given the palpable prostate finding which may indicate need for comprehensive genitourinary evaluation 1