Renal artery stenosis (RAS) is the narrowing of one or both renal arteries. “Renal” means “kidney” and “stenosis” means “narrowing.” The renal arteries are blood vessels that carry blood to the kidneys from the aorta – the main blood vessel that carries blood from the heart to arteries throughout the body.
Renovascular hypertension (RVH) is high blood pressure caused by RAS. A person’s blood pressure is considered normal if it stays at or below 120/80.
What causes RAS?
About 90 percent of RAS is caused by atherosclerosis NIH external link—clogging, narrowing, and hardening of the renal arteries.2 In these cases, RAS develops when plaque—a sticky substance made up of fat, cholesterol, calcium, and other material found in the blood—builds up on the inner wall of one or both renal arteries. Plaque buildup is what makes the artery wall hard and narrow.
Most other cases of RAS are caused by fibromuscular dysplasia (FMD)—the abnormal development or growth of cells on the renal artery walls—which can cause blood vessels to narrow. Rarely, RAS is caused by other conditions.
Who is at risk for RAS?
People at risk for artherosclerosis are also at risk for RAS. Risk factors for RAS caused by artherosclerosis include
· high blood cholesterol levels
· high blood pressure
· lack of physical activity
· a diet high in fat, cholesterol, sodium, and sugar
· being a man older than 45 or a woman older than 55
· a family history of early heart disease
The risk factors for RAS caused by FMD are unknown, but FMD is most common in women and people 25 to 50 years of age.3 FMD can affect more than one person in a family, indicating that it may be caused by an inherited gene.
How is RAS diagnosed?
A health care provider can diagnose RAS by listening to the abdomen with a stethoscope and performing imaging tests. When blood flows through a narrow artery, it sometimes makes a whooshing sound, called a bruit. The health care provider may place a stethoscope on the front or the side of the abdomen to listen for this sound. The absence of this sound, however, does not exclude the possibility of RAS.
The following imaging tests are used to diagnose RAS:
· Duplex ultrasound.
· Catheter angiogram
· Computerized tomographic angiography (CTA) scan.
· Magnetic resonance angiogram (MRA).
How is RAS treated?
Treatment for RAS includes lifestyle changes, medications, and surgery and aims to
· prevent RAS from getting worse
· treat RVH
· relieve the blockage of the renal arteries
RAS that has not led to RVH or caused a significant blockage of the artery may not need treatment. RAS that needs to be treated, also called critical RAS, is defined by the American Heart Association as a reduction by more than 60 percent in the diameter of the renal artery.1 However, health care providers are not exactly sure what degree of blockage will cause significant problems.
The first step in treating RAS is making lifestyle changes that promote healthy blood vessels throughout the body, including the renal arteries. The best ways to keep plaque from building up in the arteries are to exercise, maintain a healthy body weight, and choose healthy foods. People who smoke should quit to help protect their kidneys and other internal organs.
Two types of blood pressure-lowering medications, angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs), have proven effective in slowing the progression of kidney disease. People with RAS who are prescribed an ACE inhibitor or ARB should have their kidney function checked within a few weeks of starting the medication.
A cholesterol-lowering medication to prevent plaque from building up in the arteries and a blood-thinner, such as aspirin, to help the blood flow more easily through the arteries may also be prescribed.
Surgery may be recommended for people with RAS caused by FMD or RAS that does not improve with medication.
Angioplasty and stenting.
Endarterectomy or bypass surgery.
Eating, Diet, and Nutrition
Limiting intake of fats, cholesterol, sodium, and sugar can help prevent atherosclerosis, which can lead to RAS. Most sodium in the diet comes from salt.
More information about nutrition for CKD is provided in the NIDDK health topics, Eating Right for Chronic Kidney Disease and Nutrition for Advanced Chronic Kidney Disease in Adults. People should talk with their health care provider about what diet is right for them.