Acute kidney injury

Acute kidney injury (AKI) was previously known as acute renal failure (ARF), acute kidney failure or acute renal insufficiency. With AKI, kidney function decreases rapidly – usually within a period of two days. In severe cases, kidney function may completely stop.

The kidneys clean the blood, removing the by-products of metabolism. They produce urine, in which these waste products are normally excreted from the body.

If the kidneys stop functioning normally, there is a build-up of these substances in the blood. This results in uremia or uremic toxicity, which, at an advanced stage, can be life-threatening. There is also an accumulation of fluid in the body’s tissues (edema). 

Acute injury of the kidneys may occur if a person loses lots of blood in an accident. 

Certain medication or pre-existing conditions can also have a limiting effect on kidney function.

Acute kidney injury can usually be reversed if it is detected and treated in time.

Acute kidney injury often goes unnoticed. However, the first sign may be decreased urine output.

Other symptoms occur if complications arise.

As fluid becomes backed up in the body, it increasingly accumulates in the bodily tissue – this usually begins in the legs in particular. Later, fluid may also build up in the lungs (pulmonary edema), leading to breathing problems. There may also be a collection of fluid in the abdomen (ascites).

Fatigue, headache, nausea and vomiting may be signs that the products of metabolism are no longer being removed from the body in the urine and are instead building up inside the body.

This build-up of toxins in the blood is known as uremia or uremic toxicity. Other signs include itching of the skin and a brownish-yellow skin tone. In some cases, the breath smells like urine or the person suffers muscle cramps. As the condition progresses, patients often become confused. They may also experience epileptic seizures or a loss of consciousness or enter into a coma.

Doctors place the causes of acute kidney injury into three categories – prerenal (occurring before the blood reaches the kidneys), intrarenal (occurring in the kidneys) and postrenal (occurring downstream of the kidneys).

Prerenal AKI

Prerenal causes, i.e., those occurring before the blood reaches the kidneys, lead to an impaired blood flow to these organs. These causes are responsible for about 60% of cases.

They may be due to a severe reduction in blood flow – for example, with a major hemorrhage in an accident, widespread burns or due to severe, persistent diarrhea and vomiting. Prerenal kidney injury may also occur as a result of a heart attack if blood pressure suddenly drops because the heart is no longer pumping normally. 

Intrarenal AKI

With intrarenal causes, the kidney itself is damaged. Around 35% of cases of AKI are intrarenal.

The most common cause is acute tubular necrosis. When this happens, part of the tissue in the kidney known as the tubular system is damaged. This may be caused by reduced blood flow to the kidneys. If this situation persists, tubular cells may begin to die. 

Drugs like antibiotics, heavy metals and inflammation can also damage the kidneys themselves. 

Postrenal AKI

Postrenal kidney injury, in which the causes arise downstream of the kidneys, is the least common type of acute kidney injury – making up just 5% of cases. Kidney stones and ureteral stones, tumors, blood clots or blockages of the urethra prevent sufficient flow of urine. 

Up to 7% of people attending hospital are diagnosed with acute kidney injury. 

People with acute kidney injury often make a full recovery, provided that they are treated in time.

However, around 15% of people require long-term dialysis. Dialysis replaces the functioning of the kidneys and removes harmful toxins from the blood.

The outlook for people with AKI also depends on its cause. If doctors can promptly treat heavy blood loss after an accident, kidney function will usually return to normal. 

The age of the patient and the duration of the condition are other factors affecting outlook.

Some complications also make a severe form of the condition more likely to develop. These include hyperkalemia, where there is a build-up of potassium in the blood. This can lead to life-threatening cardiac arrhythmias (irregular heartbeat).

Fluid may also accumulate in the tissues, leading to pulmonary edema (fluid build-up in the lungs), for example.

People who are at a high risk of developing AKI have regular hospital screening to determine the level of creatinine in their blood.

When the kidneys are working normally, creatinine is removed in the urine. With acute kidney injury, this by-product of metabolism remains in the body and increases in the blood. If the level rises within a short space of time, this is an indicator of acute kidney injury.

To detect AKI, doctors measure the volume of urine excreted by a patient. If it drops below a certain level, this indicates an acute condition. 

The level of creatinine in the blood can also be measured. Once this rises above a certain value, this similarly indicates AKI.

The cause of acute kidney injury is sometime obvious – as in the case of a severe hemorrhage. If not, additional blood and urine tests are needed. An ultrasound scan can reveal the presence of a tumor or kidney stones as the cause. A tissue sample (biopsy) is also required in some cases.

The treatment options for acute kidney injury depend on the cause. 

It is important for the fluid levels in the body to be maintained at a healthy balance. If there is too much fluid in the body, this can sometimes cause life-threatening swelling in the tissues (edema). However, kidney tissue may be damaged if there is too little fluid. In this case, patients can be given fluid in the form of an infusion.

If acute kidney failure occurs as a result of the patient taking certain medication, doctors will investigate whether a different drug can be used instead or the dose adjusted.

If the patient is unable to pass urine because of kidney stones or ureteral stones, these have to be removed. 

If treatment takes a long time and kidney function remains limited, kidney replacement therapy in the form of dialysis may be considered. 

Sometimes, the kidney is so damaged that permanent dialysis is required. Doctors may also recommend a kidney transplant.

Following treatment, it is important for people to have their kidney function tested regularly by their family doctor. 

This is especially true for people who are at an increased risk of chronic kidney diseases. These include older people and those with chronic kidney problems. 

Self-help groups offer people with a chronic kidney disease a means of finding information, getting advice and sharing personal experiences. 

You can find suitable self-help groups through the database provided on the website of the National Contact and Information Point for Encouraging and Supporting Self-Help Groups (NAKOS).