Your doctor will try to find out what has caused your child’s kidneys to not work as normal. AKI may be related to other health conditions or problems. In some children, there is more than one cause.
Types of AKI
There are three types of AKI, depending on what has caused the kidneys to stop working:
Pre-renal AKI
This happens when there is not enough blood flow to the kidneys because your child’s blood pressure is too low. This can be caused by:
- Dehydration, when there is not enough water in the body. This can happen in children who have severe vomiting or diarrhoea, because they lose a lot of water. If your child has severe vomiting or diarrhoea, your doctor may advise you to stop giving your child medicines which can make the problem worse like:
- non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen
- medicines that lower blood pressure (called ACE inhibitors and Angiotensin receptor blockers)
- medicines that help flush out extra water (called diuretics).
- A large amount of bleeding (haemorrhage) – for example, after a serious injury
- An infection in the blood (septicaemia)
- Nephrotic syndrome – when the kidneys leak a lot of protein in the urine, causing water to leak into the tissues from the blood and parts of the body to swell (oedema)
- Other conditions, including hepatorenal syndrome (when the liver stops working) and heart failure (when the heart cannot pump as much blood around the body)
Renal AKI
In renal AKI, there is a problem inside the kidneys. It is also called intrinsic or intra-renal AKI and can be caused by:
- Conditions that affect the kidney
- Haemolytic uraemic syndrome (HUS) is the most common cause of renal AKI in children. It usually happens after an infection in the gut, when children also get diarrhoea. Most children recover from these infections, but some get HUS. When a part of the body is damaged, the body makes blood clots, which are like clumps of blood. These help heal wounds, such as a cut in the skin. In HUS, the body makes blood clots in the wrong places, and these can damage the kidney.
- Glomerulonephritis is a group of diseases where the tiny filters of the kidney (the glomeruli) are damaged. Children with glomerulonephritis have blood and protein in their urine, and may get swelling of their body, especially around the face and legs.
- Interstitial nephritis (also known as tubulo-interstitial nephritis), where parts of the kidney become inflamed (swollen). These include the renal tubules, the long tubes that carry the liquid that will become urine. This causes pressure to rise inside the kidneys. There is less blood flow into the kidney, which leads to AKI. It is often not possible to know why the inflammation happens. But, in some children, certain medicines can lead to interstitial nephritis.
- Other problems affecting the kidneys
- Acute tubular necrosis (ATN) which is when the kidneys do not get enough oxygen from the body. This damages the renal tubules so they stop working.
- Renal vein thrombosis when the renal vein, the blood vessel that carries blood out of the kidney, is blocked with a blood clot.
- Conditions that affect different parts of the body
- Vasculitis – the blood vessels become inflamed or swollen, especially in the skin. Some types of vasculitis also affect the blood vessel including the kidneys.
- Hepatitis – the liver becomes inflamed. This causes changes in chemicals in the blood, which can lead to AKI.
- Tumour lysis syndrome – this is a problem that happens in some children who are being treated for cancer.
- Rhabdomyolysis – this means there is a rapid breakdown in muscle cells. The substances from this breakdown are released into the blood stream too rapidly for the kidneys to remove them and can cause damage to the kidney.
Post-renal AKI
Post-renal AKI is caused by an obstruction, or a blockage, in the urinary system. This obstruction affects how urine leaves the body when we pass urine.
It often happens because of a structural problem, where one or more parts of the urinary system have not developed properly. Children with structural problems are usually born with them (congenital conditions). They are sometimes found out during an ultrasound scan before birth. Occasionally, children get structural problems later in life. These are known as acquired conditions.
Urinary system blockages include:
- Posterior urethral valves (PUV) – a blockage in the back part of the urethra (nearest the bladder) in some boys
- Pelviureteric junction (PUJ) dysfunction – a blockage between the renal pelvis (in the kidney) and the ureter
- Vesicoureteric junction (VUJ) dysfunction – a blockage between the ureter and the bladder
- Kidney stones – which may cause pain and block parts of the urinary system
Not all children who have these get AKI. The blockage needs to affect both kidneys before it can cause post-renal AKI. If a child has only one working kidney, it would need to affect that kidney.