From the Guidelines
Renal artery stenosis is diagnosed through a combination of clinical findings, laboratory tests, and imaging studies, with duplex ultrasonography serving as the initial screening test, looking for peak systolic velocity >180-200 cm/sec and renal-to-aortic ratio >3.5, as recommended by the 2024 ESC guidelines 1. The diagnostic criteria for renal artery stenosis (RAS) include:
- Hypertension that is resistant to multiple medications, especially in patients with sudden onset or worsening of previously controlled hypertension, particularly before age 30 or after age 55
- Laboratory findings may show elevated serum creatinine, decreased estimated glomerular filtration rate (eGFR), or worsening renal function after starting ACE inhibitors or ARBs
- Imaging is essential for definitive diagnosis, with the following modalities and criteria:
- Duplex ultrasonography: peak systolic velocity >180-200 cm/sec and renal-to-aortic ratio >3.5 1
- CT angiography and MR angiography: luminal narrowing >50-70% as significant, with >90% sensitivity and specificity 1
- Digital subtraction angiography: remains the gold standard, allowing for simultaneous intervention if needed, and a pressure gradient >20 mmHg across the stenosis or >10% difference in systolic pressure confirms hemodynamically significant stenosis
- Captopril renal scintigraphy: may be used in select cases, showing asymmetric function or delayed uptake in the affected kidney 1 The 2024 ESC guidelines recommend duplex ultrasonography as the first-line imaging modality in patients with suspicion of RAS, and MRA or CTA in cases of DUS-based suspicion of RAS or inconclusive DUS 1. In patients with atherosclerotic RAS, it is recommended to assess clinical high-risk features and kidney viability when evaluating renal artery revascularization 1. These criteria help identify patients who might benefit from revascularization procedures, particularly those with fibromuscular dysplasia or severe atherosclerotic disease causing progressive renal dysfunction.
From the Research
Diagnostic Criteria for Renal Artery Stenosis (RAS)
The diagnostic criteria for RAS involve various imaging modalities and techniques, including:
- Intravenous urography
- B Mode ultrasound
- Doppler ultrasound
- Renal scintigraphy with angiotensin-converting enzyme inhibitors
- Intra-venous and intra-arterial catheter angiography
- Computed tomographic angiography
- Magnetic resonance angiography 2 Specific criteria for diagnosing RAS using ultrasound include:
- Peak systolic velocity (PSV) greater than 180-200 cm/s 3
- Renal aortic ratio (RAR) 3
- Resistance index (RI) 3
- Acceleration time (AT) 3 A stenosis of 50% or more can be diagnosed if the maximal systolic velocity in the main renal artery is more than 180 cm/sec and velocity in the distal renal artery less than one quarter of the maximum velocity 4
Imaging Modalities
Different imaging modalities have their own advantages and disadvantages, including:
- Catheter angiography: considered the gold standard, but most invasive 2, 5
- Ultrasonography: safest and least expensive, but least accurate and most operator-dependent 5
- Computed tomographic angiography and magnetic resonance angiography: intermediate in terms of accuracy and expense 5
- Magnetic resonance angiography: can be used without contrast and rivals contrast-enhanced techniques in some patients 5
Detection of Significant RAS
Color Doppler sonography can be used to detect significant RAS, with a sensitivity and specificity of 96.7% and 98.0%, respectively, compared to angiography 4 Contrast-enhanced ultrasound can improve accuracy in detecting RAS 3