Renal Artery Stenosis: When-and How-to Screen?

Q:What is the best screening test for suspectedrenal artery stenosis?

A:First, let me state that renal artery stenosis is present in less than 1% ofall hypertensive patients. In young patients, particularly women youngerthan 50 years, most cases result from fibromuscular dysplasia of the renal arteries.In older patients, atherosclerotic renal artery disease is the usual cause.

Atherosclerotic renal artery stenosis is particularly common in patientswith aortoiliac occlusive disease, coronary artery disease, peripheral vasculardisease, or diabetes mellitus. The prevalence of this disorder in persons olderthan 60 years may approach 5% among those with advanced atherosclerosis.

In view of the low prevalence of renal artery stenosis, it is not economicallysound to screen for this condition in all patients with newly diagnosedhypertension. Screening has greater predictive value--and thus is more costeffective--in patients who exhibit 1 or more clinical clues that suggest renalartery stenosis.

THE WORKUP
Begin with a careful medical history and thorough physical examination,which can uncover clues such as:

• The abrupt onset of hypertension before age 30, particularly in youngwomen, or after age 55 years in men or women.
• Accelerated or malignant hypertension.
• Hypertension refractory to an appropriate triple-drug regimen, including a diuretic.
• A continuous systolic/diastolic epigastric or flank bruit.
• A unilateral small kidney identified by any previous study.
• Moderate hypertension in a patient with diffuse atherosclerosis (eg, in the carotid, coronary, and peripheral arteries).
• Unexplained azotemia in the presence of mild to moderate hypertension.
• Azotemia induced by an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker.
• Acute pulmonary edema in the presence of hypertension, azotemia, and diffuse atherosclerotic vascular disease.
• Azotemia, with or without hypertension (particularly with a normal urinary sediment).

Consider for further evaluation patients who have 1 or more of theabove signs.

NONINVASIVESCREENING STUDIES
Early studies, such as measurement of peripheral plasma renin activityor captopril-stimulated renin activity, have fallen out of favor because of limitedsensitivity and specificity and, hence, poor predictive accuracy in diagnosingrenal artery stenosis--particularly among elderly patients. The preponderanceof atherosclerosis-related renal arterystenosis and the risks of invasiverenal arteriography in patients withthis condition have led to the developmentof a number of noninvasivescreening tests (Box).¹

Captopril renography. This testconsists of renal scintigraphy--usingany one of several appropriate isotopes--performed at baseline andagain 30 to 60 minutes after the patienthas ingested 25 to 50 mg of captopril. A reduced uptakeof the radionuclide and prolonged time to maximalactivity after captopril administration indicate delayed excretionand possibly renal artery stenosis.

In younger patients with fibromuscular disease, captoprilrenography can identify critical arterial stenosis witha sensitivity and specificity of greater than 90%. Diagnosticaccuracy is limited in patients with atherosclerotic renalartery stenosis in the presence of azotemia. In addition,hypertension in older patients may not be renin-dependent;in this setting, the results would not accurately predictthe course of hypertension following an interventionto correct the stenosis.

Renal duplex ultrasonography. This procedure combinesdirect B-mode imaging with Doppler measurementsof the velocity of blood flow. It provides both anatomic andfunctional assessments of the degree of stenosis, as wellas measurement of kidney size. Another advantage is thatthis study requires no contrast material and is thereforesafe in patients with impaired renal function. It is also usefulfor serial follow-up after intervention.

Results correlate well with those of renal angiographyin centers where the procedure is done with care andaccuracy. Unfortunately, the technique is highly dependenton operator skill and may be less reliable in obesepersons. It also does not provide information on accessoryrenal arteries. The availability of high-quality studies ofthis procedure is still limited.

CT angiography. This technique provides excellentimages of the renal arteries and major branches as well asthe perirenal aorta. Unfortunately, it requires a large volumeof contrast medium, which makes it potentiallynephrotoxic, particularly in older patients with atheroscleroticrenal artery stenosis and azotemia.

Magnetic resonance angiography (MRA). This techniqueis entirely noninvasive and uses no radiation. It hasexcellent sensitivity and specificity in identifying the mainrenal arteries and perirenal aorta. Enhancement of imageswith gadolinium, which is not nephrotoxic, can further increasesensitivity and specificity. Respiratory artifact, peristalsis,tortuous vessels, and turbulent flow can limit theclarity of images. Up to 10% of patients may be unable toundergo screening because of anxiety related to confinementin the machine.

References:

REFERENCES:1. Vidt DG. Screening for renal artery stenosis: which patients? which test?Cleve Clin J Med. 2000;67:318-320.
2. Vasbinder GB, Nelemans PJ, Kessels AG, et al. Diagnostic tests for renalartery stenosis in patients suspected of having renovascular hypertension: ameta-analysis. Ann Intern Med. 2001;135:401-411.