Dialysis is often used to replicate the functions of the kidneys while a person is waiting to have a kidney transplant.

How the kidneys work

The kidneys contain millions of tiny filters called nephrons. As blood passes through the kidneys, nephrons filter out waste products and excess fluid which are later passed out of the body as urine.

However, if the nephrons become damaged, the kidneys can lose their filtering ability and dangerous levels of fluid and waste products can build up.

Kidney failure occurs when the kidneys have lost about 90% of their filtering ability. Left untreated, the amount of waste products in the blood will build up to a dangerous level, resulting in coma and death.

Kidney transplant

A kidney transplant is the best way to treat kidney failure. However, it can often take a number of months or years before a suitable donor kidney becomes available. In the meantime, dialysis can be used.

Some people with kidney failure are unable to have a kidney transplant because they have another serious health condition, such as heart failure or cancer. This makes it unlikely that they would survive the transplant procedure.

If you are not suitable for a kidney transplant, you will need to have dialysis for the rest of your life.

Common causes of kidney failure

Common causes of kidney failure include:

• diabetes 
• glomerulonephritis (chronic inflammation of the kidneys)
• high blood pressure (hypertension)

These are described in more detail below.

Diabetes

If you have diabetes, your body either does not produce enough of a hormone called insulin (type 1 diabetes), or it does not make effective use of insulin (type 2 diabetes).

Insulin is vital because it breaks down blood sugar (glucose) to produce carbohydrate, which provides energy.

If you have poorly controlled diabetes, too much glucose can build up in your blood. The excess glucose can damage the tiny filters (nephrons) inside your kidneys.

The damaged nephrons can prevent your kidneys from filtering out excess fluid and waste products from your blood.

Glomerulonephritis

In glomerulonephritis, tiny structures inside the kidneys, known as glomeruli, become inflamed.

Glomeruli are an important part of the kidney's filters (nephrons). If they keep getting inflamed, they can become scarred. This can disrupt your kidney’s ability to filter and clean waste products from the blood.

Glomerulonephritis is sometimes caused when the body's immune system mistakes harmless proteins inside the kidneys as a threat and attacks the kidneys, leading to inflammation.

However, in many cases, there is no obvious reason why glomerulonephritis occurs.

High blood pressure

Blood pressure is a measurement of the amount of pressure required by your heart to pump blood around your veins and arteries. Too much pressure, known as high blood pressure or hypertension, can damage your body's organs and lead to heart disease.

High blood pressure also causes kidney damage by putting strain on the small blood vessels in the kidneys. This prevents the filtering process working properly.

In 90% of cases of high blood pressure, the causes are unknown. However, there appears to be a strong link between the condition and lifestyle factors, such as being overweight, having a diet that is high in salt, smoking and drinking too much alcohol.

Other causes

Other, less common causes of kidney failure include:

• polycystic kidney disease – an inherited condition where cysts (fluid-filled sacs) develop inside the kidneys
• repeated kidney infections
• renal artery disease – a condition where the arteries supplying blood to the kidneys become clogged with fatty substances called plaques; a reduced blood supply can damage the kidney’s tissues

In rare cases, blood that’s visible in the urine can signify a renal condition with a potential to progress to kidney failure. This always needs to be investigated by your doctor.

Even quite advanced cases of kidney failure can have few symptoms. This means that the problem is often only identified when blood and protein is found in urine samples or if blood test results are abnormal.