The medical name for stones in the kidneys is nephrolithiasis. They are stone-like lumps that develop in one or both of the kidneys and when these stones cause severe pain, this is known as renal colic.
You are usually born with two kidneys, which are bean-shaped organs approximately 10 cm (4 in) in length. They are located towards the back of your abdomen on either side of the spine and their function is to remove waste products from the blood. The clean blood is then transferred back into the body and the waste products are passed out of the body as urine.
The waste products in the blood can occasionally form crystals that collect inside the kidneys. Over time, the crystals may build up to form a hard stone-like lump. Once a kidney stone has formed, your body will try to pass it out of the body in urine. This means it will need to travel through the urinary system (the kidneys, the kidney tubes and then the bladder).
Small stones may pass out painlessly in the urine and may even go undetected. However, it is fairly common for a stone to block part of the urinary system, such as the ureter (the tube connecting the kidney to the bladder) or the urethra (the tube through which urine passes out of the body). If this happens, it can cause severe pain in the abdomen or groin and sometimes causes an infection in your urinary tract.
How common are they?
Kidney stones are quite common and usually affect men more than women, especially people aged 30–60 years of age. It is estimated that around 10–20% of males and 3–5% of females are affected by renal colic.
How do they form?
Kidney stones usually form following a build-up of a substance in the body, such as:
- cystine – an amino acid that helps build protein
- uric acid – a waste product produced when the body breaks down food to use as energy
Certain medical conditions, such as cancer or kidney disease, may also increase your risk of developing kidney stones, although this is usually due to the treatment given for these conditions.
You have a greater probability of developing kidney stones if you do not drink enough fluids.
Recurrent kidney stones
Around half of those who have suffered from kidney stones will experience them again within the following 10 years. You have a greater risk of developing recurrent (returning) kidney stones when you:
- eat a high-protein, low-fibre diet
- are inactive or bed-bound
- have a history of kidney stones running in your family
- only have one functioning kidney
- have had several kidney or urinary infections
- have previously had a kidney stone, particularly if you were under 25 years of age at that time
- have had an intestinal bypass (surgery on your digestive system)
- suffer from a disease of the small intestine, such as an inflammationof the gut (Crohn’s disease)
Certain types of medication may also increase your risk of developing recurrent kidney stones, including:
- vitamin D supplements
Types of Kidney Stones
A number of different factors can cause kidney stones to develop, of which there are four main types:
Calcium stones are usually either spiky and rough or large and smooth. They are the most common type of kidney stone and are caused when there is too much calcium in the urine, due to factors such as:
- high levels of vitamin D
- an overactive parathyroid gland (this gland help regulate the amount of calcium in your body)
- kidney disease
- a rare disease called sarcoidosis that causes body cells to clump together
- some rare cancers
This type of stone is more common in women than in men. They are often caused by infections, commonly occurring after a urinary tract inflammation.
Uric Acid Stones
These often form when there is a high amount of acid in your urine and may be caused by:
- eating a high protein diet that includes lots of meat
- a condition such as Gout, that prevents the body breaking down chemicals
- an inherited condition that causes higher levels of acid in the body
- chemotherapy treatment for cancer
Cystine stones are the rarest form of kidney stone, caused by an inherited condition called cystinuria, which affects the amount of acid that passes into your urine.
Treating kidney stones
Most kidney stones are small enough [less than 4mm or 0.2in in diameter] to be passed in your urine, and it may be possible to treat the symptoms at home with medication. However, small kidney stones may still cause pain that usually lasts a couple of days and disappears once the stone has been passed. If you have severe pain, your GP may inject you with a painkiller, with a second dose given after half an hour if you are still experiencing pain. An anti-emetic [anti-sickness] medication can also be injected to treat the symptoms of nausea and vomiting. You may also be given a prescription for painkillers, anti-emetics or both, to take at home.
If you are sent home to wait for your stone to pass, you may be asked to try to collect it from your urine. You can do this by filtering your urine through gauze or a stocking. The stone can be given to your GP to help determine any further treatment you may need. If your urine is yellow or brown you are not drinking enough, so you should drink enough water to make your urine colourless.
If you have a uric acid stone, you may be advised to drink around three litres of water each day to try to dissolve it. As uric acid stones are much softer than other types of kidney stone, they can be made smaller if they are exposed to alkaline fluids. You may need to take some medication to make your urine more alkaline before the uric acid stone starts to dissolve.
Larger stones (6-7mm or larger) may be too big to pass naturally, so need to be broken up with X-rays or ultrasound in hospital, or surgically removed. Depending on the size and location of your stones, the type of treatment you will receive could include:
- extracorporeal shock wave lithotripsy (ESWL)
- percutaneous nephrolithotomy (PCNL)
- open surgery
Extracorporeal shock wave lithotripsy (ESWL)
This is the most common way of treating kidney stones that cannot be passed in the urine and involves using X-rays [high-energy radiation] or ultrasound (high-frequency sound waves) to pin-point where a kidney stone is. A machine then sends shock waves of energy to the stone to break it into smaller pieces so it can be passed in your urine. ESWL can be an uncomfortable form of treatment, so it is usually performed after giving painkilling medication. Although ESWL is up to 99% effective for stones up to 20mm [0.8in], you may need more than one session to successfully treat your kidney stones.
If a kidney stone is stuck in your ureter [the muscular tube that carries waste products from your kidneys to your bladder] you may need to have ureterorenoscopy, also known as retrograde intrarenal surgery (RIRS).
This involves passing a long, thin telescope, called an ureteroscope, through your urethra (the tube that carries urine from the bladder to the outside of the body) and into your bladder. It is then passed up into your ureter to where the stone is stuck. The surgeon may either gently try to remove the stone using another instrument or use laser energy to break the stone up into small pieces so that it can be naturally passed in your urine. You may need a plastic tube called a stent to be temporarily inserted inside you, to allow the stone fragments to drain into the bladder. For stones up to 15mm [0.6in, an ureterorenoscopy is effective in 50-80% of cases. This operation is performed under general anaesthetic, so you should not drive or operate machinery for up to 48 hours after the procedure.
Percutaneous nephrolithotomy (PCNL)
PCNL is an alternative procedure that may be used for larger stones. It may also be used if ESWL is not suitable – i.e. if the person being treated is obese.
PCNL involves using a thin telescopic instrument that is called a nephroscope. An incision that leads to your kidney is made in your back. The nephroscope is passed through the cut and into your kidney. The stone is either pulled out, or broken into smaller pieces using a laser or pneumatic energy. For stones that are 21-30mm (0.8-1.2in) in diameter, PCNL is nearly 90% effective. PCNL is always performed under general anaesthetic.
It is rare for people [less than 1% of cases] to have open surgery for kidney stones nowadays. It is usually used if there is a very large stone or abnormal anatomy and involves making an incision in your back to gain access to both your ureter and your kidney, so that the kidney stone can then be removed. Open surgery is performed under general anaesthetic.
To avoid getting kidney stones, make sure you drink plenty of water each day so that you do not become dehydrated. It is most important that you keep your urine diluted to prevent waste products forming into kidney stones.