Kidney failure

Acute kidney failure (renal failure) or acute kidney injury is when your kidneys suddenly stop working properly. This means that they are unable to remove salt, water and waste products from the bloodstream.

How does the urinary system work? 

Medical conditions - Kidney failure

The urinary system consists of the kidneys, ureters, the bladder and urethra. Your kidneys filter the blood to remove waste products and produce urine. The urine flows from your kidneys down through the ureters to the bladder, where it is stored until you go to the toilet. It passes through another tube called the urethra to the outside when urinating (peeing). 

The kidneys contain around a million tiny filtering units called glomeruli. As blood flows through the tubes in the glomerulus at pressure, waste products pass through the walls of the tubes to form urine. Blood cells and other things such as protein can’t pass through the walls because they are too big. The urine then passes through small tubes (tubules) where fluids, salts and minerals are removed for recycling around the body before flowing to the ureters.  


There are many causes of acute renal failure and often these problems are divided into three groups depending on whether they affect the flow of blood to the kidneys, the kidneys themselves or the flow of urine from the kidneys. 

Problems affecting the flow of blood into the kidneys 

This is the most common cause of acute renal failure. The kidneys can’t function properly if they don’t get enough blood to filter. The most common reason for this would be dehydration due to vomiting and diarrhoea. Heart failure can also lead to acute renal failure, because the heart is unable to pump enough blood around the body. The amount of fluid in the body can also drop suddenly as a result of other conditions, such as nephrotic syndrome. 

Problems affecting the kidneys themselves  

Haemolytic uraemic syndrome (HUS) is the most common cause of acute renal failure in children. HUS causes damage to the kidneys and stops them working as they should. Other causes include inflammation of the kidneys and certain medicines. Sometimes, if we don’t know the reason for the acute renal failure, we may need to do a kidney biopsy – where a bit of tissue is taken from the kidney to examine in a laboratory. This will help us decide if additional treatment may improve your kidney function. 

Problems affecting the flow of urine from the kidneys 

These problems are usually caused by something structural rather than an illness. Some of these structural problems can be present at birth, such as posterior urethral valves, which stop the bladder from emptying. Rarely, kidney stones may be the cause.


The symptoms of acute renal failure vary from person to person and depend on what is causing it and the degree of kidney failure. Common symptoms of acute kidney failure include:

  • Passing only a small amount of urine (oliguria) or no urine at all (anuria) because the kidneys are not filtering the blood as normal.
  • The urine may become discoloured, like the colour of tea or cola drinks.
  • Puffiness (oedema), particularly in the feet and legs, swelling of the abdomen and often weight gain, caused by the kidneys not removing excess fluid from the body.
  • Tiredness (fatigue) or lack of energy (lethargy) or nausea and vomiting and symptoms of being generally unwell. 
 In very severe acute renal failure, other symptoms may develop, such as seizures or a coma.


How is acute renal failure diagnosed?

  • A doctor’s assessment (questions about your symptoms and a physical examination).
  • Blood tests to look for waste products in your blood.
  • Urine tests to look for blood and protein in your urine.  
Further tests may be needed to find out what is causing the acute renal failure. These will include ultrasound scans to check for any physical abnormalities. Occasionally a kidney biopsy is needed so that the doctor can examine the structure of the glomeruli (the filtering units). 


The aim of treatment is to remove the cause of acute renal failure if possible and to keep the amount of salts and minerals at the correct levels in your body while your kidneys recover. If you have acute renal failure, you will have to stay in hospital for close monitoring and treatment. Depending on the cause of the acute renal failure, you may need dialysis. 

Problems affecting the flow of blood into the kidneys 

Often treating the cause of reduced blood flow is enough to treat this type of acute renal failure, unless blood flow to the kidney has been restricted for long enough to cause damage. You will be given fluids by an intravenous infusion (drip). 

Problems affecting the kidneys themselves 

You may be given diuretics, which will make you pass more urine. If they don’t work, you may be given dialysis until your kidneys recover. You may need steroids to damp down the immune system. Sometimes plasma exchange is used. 

Problems affecting the flow of urine from the kidneys 

This problem is usually treated with surgery. For example, a surgeon may fix a structural problem in your kidney that is preventing urine from draining. Your kidneys should recover well within a few weeks.

Looking ahead 

How well you recover and return to normal life depends on the cause of the renal failure. In most cases, if the problem was caused by reduced blood flow to the kidneys or reduced urine flow from the kidneys, kidney function usually recovers once this has been treated. The outlook if the kidneys themselves were damaged varies from person to person. In many cases, kidney function will recover but this may not be complete and may take some time.

Last review date:
July 2014