What ultrasound check is used for the kidney, ureters (Ureters), and bladder (Bladder)?

Renal and Urinary Tract Ultrasound

The ultrasound examination used to evaluate the kidneys, ureters, and bladder is called a "KUB ultrasound" (kidneys, ureters, and bladder ultrasound) or "renal ultrasound," which should include grayscale imaging of both kidneys and the bladder, with targeted color Doppler assessment when indicated. 1, 2

Technical Specifications

The examination should include:

• Both kidneys imaged in longitudinal and transverse planes using a curved array abdominal probe with frequency range of 2-5 MHz 1
• Bladder imaging as an integral component of the complete urinary tract evaluation 1
• Color Doppler imaging for assessment of twinkling artifact (appearing as intense multicolored signal deep to a stone) and to increase sensitivity for detecting conditions like acute pyelonephritis 1

Primary Clinical Applications

The American College of Radiology recommends ultrasound as the initial imaging modality for:

• Suspected obstructive uropathy and acute urinary retention due to its non-invasive nature, rapid deployment, and absence of radiation exposure 2
• Evaluation of hydronephrosis with sensitivity >90% and specificity of 95-100% for detecting and grading hydronephrosis 3, 2, 4
• Suspected urolithiasis in specific populations including pediatric patients and pregnant women to avoid radiation exposure 2

Diagnostic Performance

For renal pathology, ultrasound demonstrates:

• Renal stones: 81% sensitivity and 100% specificity, though stones <3mm are usually not identified 3, 4
• Ureteric stones: Only 45-46% sensitivity when used alone, increasing to 77% when combined with plain radiograph (KUB) 4, 5
• Hydronephrosis: 93% sensitivity and 100% specificity 4

Critical Limitations

Important caveats when interpreting renal ultrasound:

• Ultrasound plays no role in diagnosing ureteral injury in trauma settings 1
• Absence of hydronephrosis does not rule out ureteral stones, especially small ones 1
• Dehydration may mask obstruction 1
• Technical limitations include patient habitus, bowel gas, abdominal tenderness, and empty bladder 3, 2
• Anatomical variations (duplicated collection systems, horseshoe kidney, ectopic kidney) may be mistaken for pathology 1, 3

Special Populations

In pregnant patients:

• Ultrasound is the imaging modality of choice due to absence of radiation 2
• Physiologic hydronephrosis occurs in >80% of pregnant patients in second and third trimester, making hydronephrosis alone unreliable for diagnosing acute pyelonephritis 1

In pediatric patients:

• Ultrasound is the preferred initial imaging modality to avoid radiation exposure 2
• Usually appropriate for initial evaluation of microscopic hematuria with proteinuria and nonpainful macroscopic hematuria 2

When Ultrasound Is Insufficient

In trauma settings, ultrasound is generally not recommended:

• Contrast-enhanced CT with delayed urographic phase is the gold standard for evaluating kidney, ureter, and bladder injuries in hemodynamically stable trauma patients 1
• Retrograde cystography (conventional or CT) represents the diagnostic procedure of choice for bladder injuries, as it is more sensitive and specific than CT with delayed phase 1