Acute kidney injury or acute renal failure is a sudden deterioration in kidney function that develops rapidly and is potentially reversible.

Chronic kidney disease, also known as chronic renal failure, develops more gradually as a result of kidney damage over a longer period of time and may be stabilised. End-stage renal failure is an irreversible loss of kidney function.

What can cause acute kidney failure?

The kidney is responsible for cleaning the blood. Blood passes into the kidney, useful substances are retained, and then the waste and water that is left passes out to the bladder. Urine, the fluid that is produced, then leaves the body. If the kidneys fail, waste builds up to dangerous levels, causing serious health problems.

The causes of acute kidney failure can be divided into 3 categories according to where the underlying problem occurs:

  • pre-renal (problems that prevent blood getting to the kidney)
  • renal (in the kidney itself)
  • post-renal (problems that prevent urine exiting the kidney)

Pre-renal causes of kidney failure

Pre-renal kidney failure occurs when the kidneys do not receive enough blood and accounts for between 60 % and 70 % of cases of acute kidney failure. It can be caused by:

  • Dehydration.
  • Interruption of blood flow to the kidneys as a result of a heart attack or heart failure.
  • A sudden and sustained drop in blood pressure.
  • Sepsis, an infection that spreads through the blood.
  • Narrowing or blockage of the arteries that lead to the kidney.
  • Liver failure as this prevents the body being able to control blood flow to other organs.

Renal causes of kidney failure

These account for 25 to 40% of cases of kidney failure and are due to problems within the kidney. These include:

  • Diseased blood vessels or blood clots inside the kidney.
  • Damage to the kidney caused by toxins: poisons, illegal drugs and as a side effect of prescribed drugs such as chemotherapy, antibiotics and radio contrast agents.
  • Inflammation of the kidney, which may be the consequence of a systemic disease or a disease which selectively affects the kidney (glomerulonephritis, acute interstitial nephritis), and/or acute tubular necrosis (death of the tubular cells within the kidney).

Post-renal causes of kidney failure

Post-renal kidney failure occurs when the flow of urine out of the kidneys is disrupted, and this is sometimes called obstructive renal failure. Post-renal kidney failure accounts for between 5 % and 10 % of all cases and is generally reversible providing the problem is removed before there is lasting damage to the kidneys.

The exit of urine can be obstructed by:

  • Kidney stones.
  • Bladder stones.
  • Cancers in the urinary tract or nearby structures.
  • An enlarged prostate.
  • Nerve damage in the nerves that control emptying of the bladder.

What are the causes of chronic kidney disease?

Chronic kidney disease can occur as a result of an underlying chronic condition, or simply as a result of an age-related decline in kidney function. Common causes of chronic kidney disease include:

  • Diabetes.
  • High blood pressure.
  • Other chronic diseases affecting multiple systems, for example systemic lupus erythematosus (SLE, or lupus) and systemic vasculitis.
  • Inflammation within the tissues of the kidneys (glomerulonephritis or acute interstitial nephritis).
  • Inherited diseases, such as polycystic kidney disease.
  • Renovascular disease, which is the narrowing or obstruction of the renal blood vessels.
  • Ingestion of drugs or other toxins, including over-the-counter painkillers.

In many cases, the original cause of chronic kidney disease cannot be identified.

What are the symptoms of kidney failure?

Acute kidney injury is often the result of an acute illness or trauma and the cause is usually obvious. If you are in a car accident, for example, and you lose a lot of blood, this can reduce the amount of blood getting to the kidneys, causing acute kidney failure. Severe dehydration caused by excessive vomiting and diarrhoea due to severe food poisoning can also cause blood pressure to fall.

In chronic kidney disease, the early kidney damage that leads to eventual kidney failure can be ‘silent’, without causing any symptoms in the early stages.

In both chronic and acute kidney disease, the symptoms specifically related to kidney failure are similar and include:

  • High blood pressure
  • Decreased urine production
  • Water retention and swelling of the body tissues
  • Abdominal or back pain
  • Tiredness
  • Weakness
  • A metallic taste in the mouth
  • Mental confusion
  • Nausea/vomiting and/or diarrhoea
  • Itching
  • Breathlessness
  • Seizures or coma in severe acute cases.