Kidney disease and high blood pressure

High blood pressure can damage your kidneys and kidney damage can raise your blood pressure.

Your blood pressure and your kidneys can affect each other. As kidney disease can raise your blood pressure, the biggest risk for people with kidney disease is not in fact kidney failure, it is developing heart disease or stroke. Looking after your blood pressure will help to keep your kidneys healthy.

What is kidney disease?

The term kidney disease describes a set of problems where the kidneys aren’t working as well as they should. You might also hear it called chronic kidney disease (CKD). It’s often mild, has no symptoms and can be managed by you and your GP, but rarely it becomes more advanced, leading to kidney failure and other serious health problems.

What do the kidneys do?
Your kidneys play an important role in removing waste products from your body and in controlling your blood pressure. They act as a filter for your blood, sifting out excess water, waste products and toxins and removing them from your body in your urine (wee). If your kidneys aren’t working properly, fluid and waste products can build up in your body.

The kidneys help to control blood pressure by removing water and salt from the blood, as well as producing hormones that are involved in controlling blood pressure.

The kidneys also produce other hormones which are involved in maintaining healthy red blood cells and in keeping your bones healthy, and kidney disease can lead to anaemia and bone disease.

How does high blood pressure cause kidney disease?

Uncontrolled high blood pressure puts an extra strain on your blood vessels, and over time they can become narrower and stiffer. If the blood vessels leading to and within the kidneys are affected, not enough blood reaches the cells of the kidneys, so they don’t get enough oxygen and nutrients, leading to scarring of the kidney tissue. This means the kidneys are less able to do their job.

Because the kidney senses it needs more blood and oxygen, it produces hormones that drive the blood pressure even higher – this can become a vicious cycle.

What else causes kidney disease?
A number of other things can cause kidney disease or raise your risk.

• Diabetes. Along with high blood pressure, diabetes is a major cause of kidney disease. It can make your blood sugar too high, giving the kidneys extra work to do. The blood sugar also damages the tiny blood vessels in the kidneys, making them ‘leaky’, especially to protein, which can leak out into your urine
• High cholesterol. This can cause a build-up of fat in the arteries, making them narrower and reducing the blood supply to the kidneys
• Smoking. Smoking raises your blood pressure and speeds up the process of atherosclerosis
• Age. Kidney disease becomes more common with age. Around half of people aged 75 or over have some damage to their kidneys, which is related to ageing. It usually remains mild or moderate, unless another kidney problem develops, for example diabetic kidney disease
• Other kidney problems. For example, kidney infections and polycystic kidney disease
• A family history of kidney disease. Your risk is higher if a family member has had advanced kidney disease
• Being of African, African Caribbean or South Asian descent. Kidney disease is more common in these ethnic groups

What are the signs and symptoms of kidney disease?

Like high blood pressure, early or mild kidney disease often has no signs or symptoms, so you might not know you have it. It is often picked up by a blood test done by the GP or hospital (see below). As kidney disease progresses it can have a number of signs and symptoms, including:

• changes to your wee, including changes in colour and smell, how often you need to wee, and how much liquid you pass
• swelling in your legs, hands or face
• tiredness
• feeling unwell
• loss of appetite
• feeling and being sick (vomiting)
• persistent thirst
• dry, itchy skin
• weight loss
• shortness of breath
• muscle cramps and paleness due to anaemia

See your GP if you have any of these symptoms, particularly if they are ongoing.

How is kidney disease diagnosed?

Blood and urine tests can show if your kidneys aren’t working properly. If you are diagnosed with high blood pressure or another problem which causes kidney disease, you might be offered tests to pick up kidney disease early:

• a urine test – to check for protein or blood in the urine
• a blood test – to measure how much fluid your kidneys can filter in a minute – this is your GFR or glomerular filtration rate. A low GFR means that your kidneys are not working properly

If these tests show signs of kidney damage you might have other tests to see where and how much damage there is. For example, an ultrasound scan to give an image of your kidneys, or a biopsy, where a small sample is taken and looked at under a microscope.

Chronic kidney disease (CKD) is staged as 1-5, with stage 5 CKD being the most advanced. Stage 3 CKD is considered moderate disease and this is where your GP will want to monitor you more closely. Whether or not there is protein in the urine is also important, particularly if you also have diabetes. 

How is kidney disease treated?

The treatments will depend on the cause of your kidney disease and how mild or advanced your kidney disease is. Mild kidney disease can be managed by you and your GP. The treatments generally aim to stop it getting worse and to lower your risk of heart disease and stroke.

The most important thing is to keep your blood pressure under control. Your doctor will want to make sure that it’s lower than 140/90mmHg, and in some cases as low as 130/80 mmHg.

Changes to your diet and lifestyle
A healthy lifestyle will help to keep your blood pressure and your kidneys healthy. For example, stopping smoking, being active, cutting down on alcohol, eating healthily and limiting the amount of salt you eat.

If your kidney disease is more advanced, your doctor may advise you to eat a special diet which reduces the amount of waste products your body produces, giving your kidneys less work to do.

Don’t use salt substitutes such as Lo-Salt or SALTernative if you have kidney disease. They contain a lot of potassium and, if your kidneys aren’t working properly, potassium can build up which leads to further problems.

Medicines
You might need medications to control your blood pressure, including ACE inhibitors and angiotensin receptor blockers. These can lower the risk of heart disease and stroke and help prevent damage to your kidneys. You might also need medications called statins for high cholesterol, insulin for diabetes, and medicines to prevent blood clots.

Dialysis
If you kidney disease is advanced, you might need dialysis. This is a procedure that performs many of the functions of the kidneys including removing waste products from the blood.

Kidney transplant
This is sometimes necessary in advanced kidney disease, but is only possible in those who are fit enough for the operation.

How can I lower my risk of kidney disease?

The changes you can make to your lifestyle to lower your blood pressure will help to lower your risk of kidney disease, for example, eating healthily, being active, stopping smoking and keeping to a healthy weight. In particular, try to eat less than 6g of salt a day.

It’s also important to make sure any health problems you already have are well controlled, including diabetes.

You can get an idea of the health of your kidneys with this online questionnaire. Finding out if you have kidney disease, or are at risk, means you can start taking steps to prevent it or stop it getting worse.

You can also find out if you are at risk of diabetes, use this questionnaire, visit your GP or get an NHS Health Check.

Read more
Our Trustee Dr Rebecca Suckling is a Consultant Nephrologist and looks after people with kidney disease. She explains more about how the kidneys and blood pressure are related, in the Winter 2017 issue of Positive Pressure. 

Information and support for people living with kidney disease, including a counselling service, online community and financial support.

Kidney Care UK. Information and support for people living with kidney disease, including a counselling service, online community and financial support.

Kidney Research UK. Information on kidney diseases.

The National Kidney Federation (NKF) is the largest Kidney Patient charity in the UK. It is run by kidney patients for kidney patients, their information includes stories from other patients.

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