Can high blood pressure damage the kidneys?

The short answer

High blood pressure (hypertension, or presha) is one of the two most common causes of chronic kidney disease (CKD) worldwide, along with diabetes. The damage usually happens slowly, over years, and without symptoms. Kidney disease can also cause blood pressure to rise. Understanding this two-way link helps explain why doctors check the kidneys of people with high blood pressure, and check the blood pressure of people with kidney disease.

How high blood pressure harms the kidneys

Your kidneys receive a large share of the blood your heart pumps. Inside each kidney are around a million tiny filtering units. Each one has a small knot of very fine blood vessels, called a glomerulus, where waste and extra fluid are filtered out of the blood.

These vessels are delicate. When blood pressure stays high for a long time:

• the walls of the small arteries leading to the filters thicken and narrow, so less blood reaches them
• the filters themselves are put under extra strain and can be damaged
• damaged filters may start to let albumin, a protein, leak into the urine
• over time, some filters scar and stop working, so the kidneys filter less blood overall

The kidneys have a lot of spare capacity, so this loss can go on for a long time before it shows up, and even then it usually shows up in tests rather than as symptoms.

How kidney disease raises blood pressure

Healthy kidneys are one of the body's main controllers of blood pressure. They do this in two ways:

• Salt and water balance. The kidneys decide how much salt and water to remove in the urine. Damaged kidneys may hold on to more, which increases the amount of fluid in the blood vessels and raises pressure.
• Hormones. The kidneys release hormones, such as renin, that tighten or relax blood vessels. When the kidneys are damaged, these signals can push blood pressure up.

This is why high blood pressure is very common in people with CKD, whatever caused their kidney disease in the first place.

The two-way cycle

Put together, the two links can form a cycle: high blood pressure damages the kidneys, damaged kidneys raise blood pressure, and higher blood pressure causes more damage. Breaking this cycle is one of the main aims of care. KDIGO has a dedicated guideline on managing blood pressure in people with CKD for this reason.

Are there warning signs?

Usually not in the early stages. Most people with high blood pressure feel well, and early kidney damage causes no pain. Swelling of the feet or ankles, foamy urine or tiredness can appear later, but they have many other possible causes. See swollen feet and foamy urine for more. The reliable way to know how the kidneys are doing is to test them.

How kidney damage is looked for

Two tests are used together:

• Urine ACR (albumin to creatinine ratio) looks for albumin leaking into the urine, often one of the earliest signs of damage. About urine ACR.
• Blood creatinine with eGFR. The lab turns creatinine into an eGFR using a validated equation, as an estimate of how well the kidneys filter. About eGFR.

A doctor may also check the urine for blood. CKD is only diagnosed when abnormal results last more than three months, so tests are usually repeated. One high creatinine result does not on its own mean kidney damage. If that is your situation, see high creatinine and high blood pressure.

Can the damage be slowed?

For many people, finding kidney changes early gives time to reduce further harm. Keeping blood pressure within the range agreed with a doctor is one of the main ways clinicians aim to protect the kidneys. Doctors may discuss certain classes of blood pressure medicine that also help protect the kidneys, especially when there is albumin in the urine. Other parts of care often include regular tests, not smoking, staying active, and advice about salt in food.

The right approach depends on your results and your overall health. Please do not start, stop or change any medicine without speaking to your doctor.

Next steps

If you have high blood pressure and have never had your kidneys checked, it is reasonable to ask your doctor about a urine ACR and a creatinine with eGFR. In Mombasa, these are available from many labs and hospital outpatient clinics, and most people take the printed results to a general doctor or physician. Read high blood pressure and your kidneys for questions to ask, or see kidney testing in Mombasa.

This page explains what a test or condition involves. It is not a diagnosis and does not replace advice from a doctor who knows your history. Your results should be interpreted together with your symptoms, other tests and a clinical assessment. Medical disclaimer.