What is the most appropriate next investigation for a male patient with hematuria and right flank pain?

Most Appropriate Next Investigation for Hematuria with Flank Pain

The most appropriate next investigation is B. CT-KUB (non-contrast CT of kidneys, ureters, and bladder). This patient presents with macroscopic hematuria and right flank pain, which strongly suggests urolithiasis as the primary differential diagnosis, and CT-KUB is the gold standard imaging modality for this clinical scenario.

Clinical Reasoning

This patient's presentation of gross hematuria with unilateral flank pain in the absence of infection creates a high clinical suspicion for urolithiasis, even though stones can present without hematuria in some cases 1. The combination of these symptoms mandates imaging evaluation to identify the underlying cause and guide appropriate management.

Why CT-KUB is the Correct Choice

• CT has superior diagnostic accuracy with sensitivity and specificity both exceeding 90% for detecting urinary tract stones, making it the gold standard for evaluating painful hematuria 2, 1
• Non-contrast CT is specifically indicated when there is high clinical suspicion for urolithiasis, as it can detect stones of all compositions, quantify stone burden, and identify complications such as hydronephrosis 2
• CT provides comprehensive evaluation beyond just stones, including assessment for renal masses, UPJ obstruction, and other anatomic abnormalities that could cause this presentation 2
• The American College of Radiology specifically recommends either ultrasound or CT as appropriate initial imaging for painful hematuria with suspected urolithiasis, with CT being more definitive 2, 1

Why Other Options Are Inappropriate

Urine cytology (Option A) is not indicated in the initial evaluation of painful hematuria. Cytology is primarily used for detecting urothelial malignancy in asymptomatic hematuria or when there is high suspicion for bladder cancer, not in acute presentations with flank pain 3, 4.

Retrograde urethrogram (Option C) is specifically indicated for suspected urethral injury in trauma settings or evaluation of urethral stricture disease, not for hematuria with flank pain 2, 3.

Cystoscopy (Option D) is indicated for persistent unexplained hematuria after negative imaging, or when there is high suspicion for bladder pathology. However, it should not be the first-line investigation in a patient with flank pain suggesting upper tract pathology 2, 3. Cystoscopy would be considered if imaging is negative and hematuria persists 2.

Important Clinical Considerations

Common Pitfalls to Avoid

• Do not dismiss the possibility of stones based on absence of hematuria alone, as a significant number of patients with urolithiasis do not have hematuria 1
• Plain radiography (KUB) is inadequate with only 59% sensitivity for stone detection and provides no information about hydronephrosis or soft tissue pathology 1
• Ultrasound has significant limitations in this setting, detecting only 75% of all urinary tract stones and only 38% of ureteral stones 2

Additional Differential Diagnoses

While urolithiasis is most likely, CT-KUB will also evaluate for:

• Renal masses or tumors that can present with hematuria and flank pain 2
• UPJ obstruction which can cause similar symptoms 2
• Alternative pathology including gastrointestinal or vascular causes, which are identified in approximately 7% of patients imaged for suspected renal colic 5

Follow-Up Based on CT Findings

• If stones are identified: Management depends on size, location, and degree of obstruction
• If CT is negative but hematuria persists: Consider cystoscopy and upper tract imaging with contrast (CT urography) to evaluate for urothelial malignancy 3
• If glomerular causes are suspected (dysmorphic RBCs, proteinuria): Nephrology referral is warranted 3, 6