Magnetic resonance angiography (MRA) and computed tomography angiography (CTA) are the most consistently accurate, noninvasive screening methods. MRA is likely the preferred option because of its lack of radiation and reduced risk of contrast media (strength of recommendation [sor]: A, large meta-analyses).
Significant renal artery stenosis (RAS) is defined anatomically as >50% stenosis of the lumen by renal angiography; stenosis is considered hemodynamically significant (potentially causing renovascular hypertension) if it exceeds 75%.1
The prevalence of renovascular hypertension among the general hypertensive population varies from 1% to 5%. The prevalence increases to 20% to 40% in the presence of certain clinical criteria:
- hypertension in patients <30 years
- worsening or sudden onset of hypertension in patients >50 years
- hypertension refractory to multiple medications
- malignant hypertension
- worsening renal function after starting an angiotensin-converting enzyme inhibitor (ACE-I).2,3 (Worsening renal function is defined as >30% decline in estimated glomerular filtration rate or >30% increase in serum creatinine during the first 2 months of ACE-I therapy.1)
Refractory hypertension associated with generalized atherosclerosis is the most predictive risk factor for RAS.
MRA is usually best, but don’t overlook ultrasound
Among the primary diagnostic tests for RAS (see TABLE W1 on page 216a), MRA is the most consistently accurate4 and least operator dependent—which makes it the best choice in most situations. One rare but serious concern with MRA is that contrast agents may cause nephrogenic systemic fibrosis (NSF), a debilitating and sometimes fatal diffuse disease affecting the skin, muscle, and internal organs. In 2006, 25 cases of NSF after exposure to gadolinium-based contrast agents were reported, prompting an FDA warning.5
Kidney duplex Doppler ultrasound can rival MRA and CTA in accuracy, but is highly operator dependent. If access to highly skilled, experienced technicians is available, this safe and less expensive option can be considered, especially for patients with chronic kidney disease.
Diagnostic tests for renovascular hypertension
|TEST||COMPOSITE RATING||SENSITIVITY||SPECIFICITY||SPECIAL CONSIDERATIONS|
|MRA||1||94%-97%4||85%-93%4||No radiation; expensive; small risk of nephrogenic systemic fibrosis from gadolinium contrast agents|
|CTA||2||88%-96%3||77%-98%3||Similar accuracy to MrA; moderate radiation exposure; requires iodinated contrast media|
|US duplex Doppler||3||0%-90%3||95%3||Noninvasive; highly operator dependent|
|ACE-I renography/scintography||4||58%-95%2||17%-100%2||Noninvasive; can be used in renal insufficiency; high radiation exposure; literature is not uniform regarding techniques and interpretation criteria|
|Invasive arteriography||5||—||—||Gold standard; invasive; better used as confirmation than screening|
|Invasive renal vein renin assays||6||65%-74%3||100%3||Good confirmatory test; invasive; possibility of sampling error|