Renal artery stenosis is a narrowing of one or both arteries that supply blood to the kidneys. This reduced blood flow triggers a chain reaction that raises blood pressure throughout the body and, over time, can damage kidney function. About 90% of cases are caused by the same fatty plaque buildup (atherosclerosis) that leads to heart attacks and strokes, making it one of the most common treatable causes of secondary hypertension.
How Narrowed Arteries Raise Blood Pressure
When blood flow to a kidney drops, specialized pressure-sensing cells in the artery walls detect the change and release an enzyme called renin. Renin kicks off a hormonal cascade: it converts a protein made by the liver into a substance that eventually becomes a powerful blood vessel constrictor. This constrictor raises blood pressure directly by tightening arteries throughout the body. It also signals the kidneys to hold onto more sodium and water, increasing blood volume and pushing pressure even higher.
On top of that, the adrenal glands respond by releasing aldosterone, a hormone that amplifies the sodium and water retention even further. The result is a self-reinforcing cycle. The kidney senses low blood flow and responds as though the entire body needs higher pressure, when in reality the problem is local, sitting right at the narrowed artery. This is why renal artery stenosis can cause blood pressure that stubbornly resists treatment with multiple medications.
Two Main Causes
Over 95% of cases fall into two categories: atherosclerosis and fibromuscular dysplasia.
Atherosclerotic renal artery stenosis accounts for roughly 90% of all cases. It develops the same way plaque builds up in heart or neck arteries, and the risk factors are the same: older age, diabetes, smoking, high cholesterol, and existing cardiovascular disease. The plaque typically forms at the opening where the renal artery branches off the aorta. Because it shares these risk factors with heart disease, people diagnosed with renal artery stenosis often have narrowing in other arteries as well.
Fibromuscular dysplasia (FMD) makes up most of the remaining cases. Instead of plaque, the artery wall itself develops abnormally, creating a beaded or ridged pattern that narrows the vessel. FMD is typically diagnosed in young to middle-aged women and rarely causes the kind of progressive kidney damage seen with atherosclerosis. It tends to affect the middle and far portions of the artery rather than the opening.
Signs and Symptoms
Renal artery stenosis often produces no symptoms on its own. Instead, it reveals itself through its consequences, most notably high blood pressure that’s unusually difficult to control. Resistant hypertension, defined as blood pressure that stays above goal despite three different blood pressure medications at full doses, is one of the classic red flags. So is needing four or more medications just to keep blood pressure in range.
Other warning signs include:
- Sudden worsening of previously stable blood pressure, especially in someone over 55 or under 30
- Unexplained decline in kidney function, particularly after starting certain blood pressure medications
- Flash pulmonary edema, episodes of sudden, severe fluid buildup in the lungs that seem to come out of nowhere
- A bruit, a whooshing sound heard through a stethoscope placed over the abdomen near the kidney area
- Asymmetric kidney size, where one kidney appears noticeably smaller than the other on imaging
None of these symptoms is unique to renal artery stenosis, which is part of what makes it tricky to identify without targeted testing.
How It’s Diagnosed
The first-line screening tool is a Doppler ultrasound of the renal arteries. It’s noninvasive, requires no radiation, and measures how fast blood is flowing through the artery. When the artery is significantly narrowed, blood speeds up as it squeezes through the tight spot, much like water through a kinked hose. A peak velocity above 200 cm per second generally indicates a stenosis of 60% or greater. In studies, Doppler ultrasound has shown a sensitivity of about 83% and specificity of 70%, meaning it catches most cases but can occasionally give false positives.
CT angiography offers a detailed look at the artery’s structure and is often used when ultrasound results are unclear. It requires contrast dye and radiation exposure, and its sensitivity runs around 67 to 68%, with specificity near 80%. MR angiography performs similarly to CT and avoids radiation, though it uses a different type of contrast agent that carries its own considerations for people with reduced kidney function.
The gold standard remains catheter-based angiography, where a thin tube is threaded into the artery and dye is injected to create a real-time X-ray image. This is typically reserved for cases where a procedure is already being planned, since it’s invasive.
What Happens if It Goes Untreated
Left alone, significant renal artery stenosis can cause the affected kidney to physically shrink. A prospective ultrasound study that tracked patients with narrowing of 60% or greater found that 26% of those kidneys lost more than 1 centimeter in length during follow-up, with an average loss of 1.9 cm. The estimated risk of this kind of measurable shrinkage was 19% within one year. By contrast, kidneys supplied by arteries with less than 60% narrowing showed no significant size loss.
This shrinkage reflects actual loss of functioning kidney tissue. As the kidney atrophies, its ability to filter blood declines, potentially progressing to chronic kidney disease. The uncontrolled high blood pressure caused by stenosis also damages blood vessels elsewhere in the body, raising the risk of heart attack, stroke, and heart failure over time.
Treatment: Medications vs. Stenting
For most people with atherosclerotic renal artery stenosis, the evidence strongly favors medication over procedures. The landmark CORAL trial, published in the New England Journal of Medicine, randomly assigned 947 patients with atherosclerotic stenosis to either medication alone or medication plus a stent (a small mesh tube placed inside the artery to hold it open). Over a median follow-up of 43 months, there was no significant difference between the two groups in rates of death, heart attack, stroke, heart failure, or progressive kidney decline. Stenting produced a modest 2 mm Hg drop in systolic blood pressure compared to medication alone, but that small difference didn’t translate into fewer clinical events.
Medical treatment typically centers on aggressive blood pressure control, cholesterol-lowering medication, and management of other cardiovascular risk factors like diabetes and smoking. One important caveat: a common class of blood pressure drugs that works by blocking the hormonal cascade described earlier is contraindicated when both renal arteries are significantly narrowed. In bilateral stenosis, these medications can cause a sharp decline in kidney function because both kidneys depend on that hormonal system to maintain adequate filtration pressure. This is one reason doctors check kidney function closely after starting or adjusting blood pressure medications.
When Procedures Are Still Considered
Stenting or angioplasty (using a balloon to widen the artery) may still be appropriate in specific situations where medication alone isn’t enough. These include recurrent flash pulmonary edema, rapidly worsening kidney function that can’t be explained by other causes, or blood pressure that truly cannot be managed despite maximum medical therapy. FMD-related stenosis also responds better to angioplasty than atherosclerotic disease does, often without needing a stent at all, and outcomes in younger patients with FMD tend to be more favorable.
The overall treatment picture has shifted significantly over the past decade. Where stenting was once routine for atherosclerotic stenosis, current practice reserves it for the subset of patients who are clearly failing on medications. For the majority, well-managed medical therapy provides equivalent protection against the major complications.