Should a 32-year-old hypertensive female with flank pain and incomplete voiding, but no dysuria, undergo a KUB (Kidneys, Ureters, Bladder) ultrasound?

Should This Patient Undergo KUB Ultrasound?

Yes, this 32-year-old hypertensive female with flank pain and incomplete voiding should undergo renal and bladder ultrasound as the initial imaging modality, even in the absence of dysuria. 1

Primary Rationale for Ultrasound

The combination of flank pain with incomplete voiding (a post-micturition symptom) warrants imaging evaluation to exclude:

• Urinary tract obstruction (stone disease, anatomic abnormalities) 1
• Hydronephrosis (which ultrasound detects with 93-100% sensitivity and specificity) 1, 2
• Structural abnormalities affecting bladder emptying 1
• Renal pathology contributing to hypertension in a young patient 3

Why Ultrasound Is the Appropriate First-Line Test

Ultrasound of the kidneys and bladder is the recommended initial imaging modality for suspected urinary tract pathology, particularly when obstruction is a consideration. 1

• The European Association of Urology (2025) explicitly states that ultrasound is the primary diagnostic tool and should not delay emergency care 1
• Ultrasound is 100% sensitive and 90% specific for diagnosing ureteral obstruction (hydronephrosis, ureterectasis, perinephric fluid) in patients with acute flank pain 1
• For renal stones, ultrasound demonstrates 81% sensitivity and 100% specificity 2
• Ultrasound can evaluate both kidneys and bladder in a single examination to assess for structural causes of incomplete voiding 1

Clinical Context: Incomplete Voiding Without Dysuria

The absence of dysuria does not exclude significant urinary tract pathology:

• Incomplete voiding is a post-micturition symptom that can indicate bladder outlet obstruction, neurogenic bladder, or anatomic abnormalities 4
• Up to 20% of patients with acute pyelonephritis lack bladder symptoms entirely 1
• Flank pain with voiding dysfunction requires evaluation for obstruction even without classic stone symptoms 1, 5
• In patients with incomplete emptying, bladder imaging is essential to assess for residual volume, masses, or structural lesions 1

Special Consideration: Young Hypertensive Patient

This patient's hypertension at age 32 adds urgency:

• Renal pathology can cause secondary hypertension through various mechanisms 3
• Flank pain with hematuria (if present) or hypertension should prompt evaluation for subcapsular hematoma, renal artery stenosis, or Page kidney 3
• Ultrasound with Doppler can assess renal perfusion and resistive indices to evaluate for vascular causes 5

Imaging Protocol Recommendations

The ultrasound examination should include:

• Both kidneys in longitudinal and transverse planes to assess for hydronephrosis, stones, masses, or parenchymal abnormalities 1
• Bladder evaluation ideally performed when distended, then reassessed post-void to measure residual volume 1
• Assessment for hydroureter and perinephric fluid 1
• Consider color Doppler if stone disease suspected, as twinkling artifact increases sensitivity for small stones to 99% 1

When to Escalate to CT

Non-contrast CT should be obtained if:

• Ultrasound findings are equivocal or negative but clinical suspicion remains high 1, 6
• Hydronephrosis is detected on ultrasound but the cause needs clarification (CT has 96-100% sensitivity for stones vs. 24-57% for ultrasound alone) 1
• Patient develops fever, worsening pain, or signs of complicated infection requiring detailed anatomic assessment 1
• Persistent symptoms beyond 72 hours despite initial management 6

Critical Pitfall to Avoid

Do not order plain KUB radiography as the initial or sole imaging test. 6, 7

• KUB has only 53-62% sensitivity and 67-69% specificity for ureteral calculi 6
• KUB is particularly insensitive for stones <4mm and mid/distal ureteral stones 6
• The American College of Radiology explicitly states that KUB is insufficient for diagnosing suspected obstruction and should not be ordered as the sole imaging modality 6
• Even though 90% of stones are radio-opaque, KUB detected only 8% of stones <5mm compared to CT 1

Algorithm for This Patient

1. Order renal and bladder ultrasound immediately 1
2. Obtain urinalysis (dipstick) and basic metabolic panel (creatinine, electrolytes) 1
3. If ultrasound shows hydronephrosis or stone: Proceed to non-contrast CT for definitive characterization 1
4. If ultrasound is negative but symptoms persist: Consider CT to exclude small stones or non-urologic causes of flank pain 1
5. Measure post-void residual during ultrasound to quantify incomplete emptying 1

The presence of incomplete voiding with flank pain constitutes sufficient indication for imaging regardless of dysuria status. 4, 5