From the Guidelines
For microscopic hematuria, a renal ultrasound is generally the preferred initial imaging study over a retroperitoneal ultrasound. A renal ultrasound specifically focuses on evaluating the kidneys and bladder, which are the most common sources of microscopic hematuria. This targeted approach allows for assessment of kidney size, structure, and detection of potential abnormalities such as stones, masses, or hydronephrosis that could explain the presence of blood in the urine. While a retroperitoneal ultrasound examines a broader area including the kidneys, adrenal glands, and surrounding structures, it may not provide the same detailed visualization of the urinary tract that is most relevant for hematuria evaluation. The renal ultrasound is also typically more readily available, less time-consuming, and sufficient as a first-line imaging test. If the renal ultrasound findings are inconclusive or additional concerns arise, further imaging such as CT urography might be warranted to complete the workup. Remember that microscopic hematuria evaluation should also include urinalysis, urine culture, and potentially cystoscopy depending on patient risk factors and persistence of findings, as recommended by the American College of Radiology Appropriateness Criteria 1.
Some key points to consider in the evaluation of microscopic hematuria include:
- The American Urological Association defines microhematuria as three or more red blood cells per high power field on microscopic evaluation of urinary sediment from a properly collected, noncontaminated urinalysis 1.
- The most common causes of hematuria can arise from anywhere along the urinary tract and are generally divided into nephrogenic and urogenic causes, with renal parenchymal disease being the most common benign nephrogenic cause of hematuria 1.
- Patients with risk factors for urinary tract cancer, such as age >35 years, smoking, or occupational exposure to chemicals, should undergo a more thorough evaluation, including CT urography if necessary 2, 3.
- Ultrasonography is recommended as the first-line imaging method by some guidelines, with CT urography reserved for higher-risk cases and those with equivocal findings in the first-line evaluation, due to concerns related to radiation exposure and cost 3, 4.
Overall, the choice of imaging study for microscopic hematuria should be guided by the patient's individual risk factors and clinical presentation, with a renal ultrasound being a reasonable initial choice in many cases, as supported by the American College of Radiology Appropriateness Criteria 1.
From the Research
Diagnostic Approaches for Microscopic Hematuria
- For patients with microscopic hematuria, the initial evaluation typically involves a combination of laboratory tests and imaging studies to determine the underlying cause of the bleeding.
- Renal ultrasound (US) is commonly used as an initial imaging modality to evaluate the kidneys and urinary tract for potential abnormalities, such as kidney stones, cysts, or tumors 5, 6.
- The sensitivity of ultrasound imaging in detecting upper urinary tract malignancy in patients with asymptomatic microscopic hematuria is high, with a sensitivity of 100% for renal cell carcinoma and upper tract urothelial cancer 6.
Comparison of Renal and Retroperitoneal Ultrasound
- There is no direct comparison between renal and retroperitoneal ultrasound in the evaluation of microscopic hematuria in the provided studies.
- However, renal ultrasound is specifically mentioned as a useful modality for evaluating the kidneys and upper urinary tract in patients with microscopic hematuria 5, 6, 7.
- Retroperitoneal ultrasound is not mentioned as a specific modality for evaluating microscopic hematuria in the provided studies.
Recommendations for Imaging Studies
- For patients over 40 with microscopic hematuria, a non-contrast computed tomography (CT) or ultrasound study should be performed 8.
- If gross hematuria is observed, cystoscopy should be added to the evaluation 8.
- The choice of imaging modality may depend on the patient's age, symptoms, and medical history, as well as the availability of imaging equipment and expertise.