Renovascular hypertension

What is renovascular hypertension?

Renovascular hypertension is high blood pressure caused by a problem with the blood supply to your kidneys. It happens when the arteries carrying blood into your kidneys become narrowed, so less blood gets through.

What are the symptoms of renovascular hypertension?

In most cases, there are no symptoms at all. That's one of the reasons the condition is hard to spot, and it's often found because of the pattern of your blood pressure readings rather than because you feel unwell.

Your doctor may suspect it if:

• your high blood pressure started before you were 30 or after you were 50
• your blood pressure was under control for a while and then suddenly rose
• your blood pressure is not coming down even though you're taking several different medicines for it.

High blood pressure that resists treatment in this way is one of the strongest clues, because renovascular hypertension is a frequent cause of it.

What causes renovascular hypertension and who is at risk?

The main cause is renal artery stenosis, which simply means a narrowing of one or both of the arteries that carry blood into your kidneys.

Two things account for most of that narrowing:

• atherosclerosis, where fatty deposits called plaque build up inside the artery wall and squeeze the channel shut
• fibromuscular dysplasia, where the cells in the artery wall grow abnormally and change the shape of the artery.

The narrowing itself doesn't raise your blood pressure directly. When less blood reaches your kidneys, they react as though your whole body is short of fluid and switch on a system of hormones known as the renin-angiotensin-aldosterone system, usually shortened to RAAS.

That system makes your body hold on to salt and water. The extra fluid fills your blood vessels, and your blood pressure goes up as a result.

Are there different types of renovascular hypertension?

The condition is usually grouped by what's causing the narrowing, because that affects who it happens to and how it's treated.

• Atherosclerotic renovascular hypertension is caused by plaque build-up. Over time, the reduced blood flow past the narrowing can also cause scarring inside the kidney, known as fibrosis.
• Fibromuscular dysplasia is caused by abnormal growth in the artery wall. Scarring inside the kidney is rare with this type, which suggests it's the fatty, inflamed environment of atherosclerosis that drives the damage rather than the narrowing alone.

You may also see the term renovascular disease. One review argues this is the more accurate description, because the blockage in the kidney arteries doesn't only raise blood pressure. It can also cause a gradual loss of kidney function as the kidney is starved of blood, known as ischaemic kidney disease.

How is renovascular hypertension diagnosed?

Because there are usually no symptoms, diagnosis starts with your doctor suspecting it from your blood pressure history. You'll then usually have a set of tests, first to check your kidneys and rule out other causes, then to look at the arteries themselves.

Blood and urine tests

• a urine test looking for protein or blood, which point to other kidney problems
• blood tests measuring urea and creatinine, which show how well your kidneys are working
• blood tests checking the balance of salts and minerals in your body
• tests of your immune system, if an autoimmune condition affecting the blood vessels is suspected.

You may also be tested for other causes of secondary high blood pressure, including hormone conditions affecting the adrenal glands.

Imaging

Several scans can show the arteries to your kidneys:

• duplex ultrasound, which uses sound waves and is often chosen first because it picks up narrowing more reliably than some older tests
• computed tomography angiography (CTA), a detailed X-ray scan of the blood vessels
• magnetic resonance angiography (MRA), which uses a strong magnet rather than X-rays.

Catheter angiography is the most accurate test available. A thin tube is passed into the artery so that the narrowing can be seen directly, and the pressure either side of it can be measured to show how much it's actually restricting blood flow.

It isn't the first choice, though. It's invasive, expensive and time-consuming, and it carries risks including tearing the artery or dislodging fatty material into smaller vessels.

How is renovascular hypertension treated?

Treatment without surgery

Treatment usually starts with medicines that lower your blood pressure, alongside changes to your diet and activity levels. The aim is both to bring your blood pressure down and to protect your kidneys from further damage.

Following your treatment plan matters here. Sticking with your medicines and lifestyle changes can slow down the loss of kidney function.

Procedures and surgery

Where medicines aren't enough, the narrowed artery can sometimes be reopened with surgery, such as:

• angioplasty, where a small balloon is used to widen the artery from the inside
• stenting, where a small mesh tube is left in place to hold the artery open, usually done at the same time as angioplasty
• surgery on the artery itself.

Not everyone benefits from these procedures, and the decision depends on how severe the narrowing is, what's causing it and how your kidneys are working. Your specialist will talk this through with you.

When should I see a doctor?

Renovascular hypertension is usually picked up during checks for high blood pressure rather than because you notice something. Having your blood pressure checked regularly is the main way it gets found.

Speak to your GP if:

• your blood pressure readings are creeping up when they were previously stable
• your blood pressure isn't coming down despite taking several medicines
• you were diagnosed with high blood pressure unusually young or unusually late in life.

If you've already been diagnosed, keep to your review appointments. Catching changes early is what protects your kidneys.