Kidney stones can develop in one or both kidneys and most often affect people aged 30 to 60.
They're quite common, with around three in 20 men and up to two in 20 women developing them at some stage of their lives.
The medical term for kidney stones is nephrolithiasis, and if they cause severe pain it's known as renal colic.
Symptoms of kidney stones
Small kidney stones may go undetected and be passed out painlessly in the urine. But it's fairly common for a stone to block part of the urinary system, such as the:
- ureter – the tube connecting the kidney to the bladder
- urethra – the tube urine passes through on its way out of the body
A blockage can cause severe pain in the abdomen or groin and sometimes causes a urinary tract infection (UTI) .
Read more about the symptoms of kidney stones .
What causes kidney stones?
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.
This is more likely to happen if you don't drink enough fluids, if you're taking some types of medication, or if you have a medical condition that raises the levels of certain substances in your urine.
Read more about the causes of kidney stones .
After a kidney stone has formed, your body will try to pass it out when you go to the toilet (in the urine). This means it will often travel through the urinary system (the kidneys, kidney tubes and bladder).
Treating and preventing kidney stones
Most kidney stones are small enough to be passed in your urine, and it may be possible to treat the symptoms at home with medication.
Larger stones may need to be broken up using ultrasound or laser energy. Occasionally, keyhole surgery may be needed to remove very large kidney stones directly.
Read more about treating kidney stones .
It's estimated that up to half of all people who have had kidney stones will experience them again within the following five years.
To avoid getting kidney stones, make sure you drink plenty of water every day so you don't become dehydrated . It's very important to keep your urine diluted (clear) to prevent waste products forming into kidney stones.
Read more about preventing kidney stones .
Very small kidney stones are unlikely to cause many symptoms. It may even go undetected and pass out painlessly when you urinate.
Symptoms usually occur if the kidney stone:
- gets stuck in your kidney
- starts to travel down the ureter (the tube that attaches each kidney to the bladder) – the ureter is narrow and kidney stones can cause pain as they try to pass through
- causes an infection
In these cases, the symptoms of kidney stones can include:
- a persistent ache in the lower back, which is sometimes also felt in the groin – men may have pain in their testicles and scrotum
- periods of intense pain in the back or side of your abdomen, or occasionally in your groin, which may last for minutes or hours
- feeling restless and unable to lie still
- nausea (feeling sick)
- needing to urinate more often than normal
- pain when you urinate (dysuria)
- blood in your urine (haematuria) – this may be caused by the stone scratching the kidney or ureter
Blocked ureter and kidney infection
A kidney stone that blocks the ureter can lead to a kidney infection. This is because waste products are unable to pass the blockage, which may cause a build-up of bacteria.
The symptoms of a kidney infection are similar to symptoms of kidney stones, but may also include:
- a high temperature (fever) of 38C (100.4F) or over
- chills and shivering
- feeling very weak or tired
- cloudy and bad-smelling urine
Kidney stones are usually formed following a build-up of certain chemicals in the body.
This build-up may be any of the following:
- uric acid – a waste product produced when the body breaks down food to use as energy
- cysteine – an amino acid that helps to build protein
Certain medical conditions can lead to an unusually high level of these substances in your urine.
You're also more likely to develop kidney stones if you don't drink enough fluids.
Recurrent kidney stones
Some people are particularly likely to keep on developing kidney stones, including people who:
- eat a high-protein, low-fibre diet
- are inactive or bed-bound
- have a family history of kidney stones
- have had several kidney or urinary infections
- have had a kidney stone before, particularly if it was before you were 25
- have only one fully working kidney
- have had an intestinal bypass (surgery on your digestive system), or a condition affecting the small intestine, such as Crohn's disease
There's evidence to suggest that certain medications may increase your risk of developing recurrent kidney stones. These include:
- diuretics (used to reduce fluid build-up)
- certain antibiotics
- certain antiretroviral medication (used to treat HIV )
- certain anti-epileptic medication
Types of kidney stones
Kidney stones can develop for a number of reasons. The causes of the four main types of kidney stone are outlined below.
Calcium stones are the most common type of kidney stone and form if there's too much calcium in the urine, which can be due to:
- an inherited condition called hypercalcuria, which leads to large amounts of calcium in urine
- an overactive parathyroid gland (the parathyroid glands help to regulate the amount of calcium in your body)
- kidney disease
- a rare condition called sarcoidosis
- some cancers
Calcium stones are usually either large and smooth or spiky and rough.
Struvite stones are often caused by infections, and they most commonly occur after a urinary tract infection that's lasted a long time.
Struvite stones are more common in women than men.
Uric acid stones
Uric acid stones can form if there's a large amount of acid in your urine. They 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 certain chemicals
- an inherited condition that causes higher than normal levels of acid in the body
Cystine stones are the rarest type of kidney stone. They're caused by an inherited condition called cystinuria, which affects the amount of acid that is passed in your urine.
Your doctor will usually be able to diagnose kidney stones from your symptoms and medical history.
It will be particularly easy if you've had kidney stones before.
You may be given tests, including:
- urine tests to check for infections and pieces of stones
- an examination of any stones that you pass in your urine
- blood tests to check that your kidneys are working properly, and to also check the levels of substances that could cause kidney stones, such as calcium
You can collect a kidney stone by urinating through some gauze or a stocking.
Having a kidney stone to analyse will make a diagnosis easier, and may help your GP determine which treatment method will be of most benefit to you.
If you have severe pain that isn't controlled by painkillers, or if you have a high temperature as well as pain, you may be referred to a urologist (a specialist in treating urinary problems).
If you're referred to hospital for an imaging test, a number of different techniques may be used. Imaging tests can help confirm the diagnosis, or identify precisely where a kidney stone is.
These tests include:
- a computerised tomography (CT) scan – where a series of X-rays at slightly different angles are taken and a computer is used to put the images together
- X-ray – an imaging technique that uses high-energy radiation to highlight abnormalities in body tissue
- an ultrasound scan – uses high-frequency sound waves to create an image of the inside of your body
- an intravenous urogram (IVU) or intravenous pyelogram (IVP) – a dye that shows up on X-ray is injected into a vein in your arm; the X-ray image highlights any blockages as the kidneys filter the dye out of your blood and into your urine
CT scans are now often used because they're thought to be more accurate (IVUs were previously the preferred imaging method). The imaging technique you have may depend on what's available at your local hospital.
Most kidney stones are small enough (less than 4mm in diameter) to be passed out in your urine and can probably be treated at home.
But even small kidney stones can be painful, although this usually only lasts a couple of days and disappears when the stone has been passed.
If you are in severe pain, your doctor can give you pain relief by injection. A second dose can be given after half an hour if you're still experiencing pain.
Medication can also be injected to treat the symptoms of nausea (feeling sick) and vomiting. This is called an anti-emetic (anti-sickness) medication.
You may also be given a prescription for painkillers, anti-emetics, or both, to take at home.
You may be advised to wait until you pass your kidney stone when you go to the toilet, and to try to collect it from your urine. You can do this by filtering your urine through gauze or a stocking.
Give the stone to your doctor so that they can have it analysed to help determine any further treatment you may need.
You should drink enough water to make your urine colourless. If your urine is yellow or brown, you're not drinking enough.
Admission to hospital
If your kidney stone has moved into your ureter (the tube that carries waste products from the kidneys to the bladder), and it's causing severe pain, your doctor may admit you to hospital for treatment.
This may be necessary if:
- you're at an increased risk of your kidneys failing (for example, because you only have one kidney)
- your symptoms don't improve within an hour of being given painkillers or anti-sickness medication
- you're dehydrated and vomiting too much to keep fluids down
- you're pregnant
- you're over 60 years of age
Treating large kidney stones
If a kidney stone is too big to be passed naturally – 6-7mm (about 0.23 to 0.27in) in diameter or larger – you may need treatment to remove it another way.
This could include:
- extracorporeal shock wave lithotripsy (ESWL)
- percutaneous nephrolithotomy (PCNL)
- open surgery
These procedures are explained in more detail below. The type of treatment you have will depend on the size and location of your stones.
Extracorporeal shock wave lithotripsy (ESWL)
ESWL is the most common way of treating kidney stones that can't be passed in the urine.
It involves using ultrasound (high-frequency sound waves) to pinpoint where a kidney stone is. Ultrasound shock waves are then sent to the stone from a machine to break it into smaller pieces, so it can be passed in your urine.
ESWL can be an uncomfortable form of treatment, so it's usually carried out after giving painkilling medication.
You may need more than one session of ESWL to successfully treat your kidney stones. ESWL is up to 99% effective for stones up to 20mm (0.8in) in diameter.
If a kidney stone is stuck in the ureter, you may need to have a ureteroscopy, which is also sometimes known as retrograde intrarenal surgery (RIRS).
It involves passing a long, thin telescope called a ureteroscope through your urethra (the tube urine passes through on its way out of the body) and into your bladder. It's then passed up into your ureter to where the stone is stuck.
The surgeon may either try to gently remove the stone using another instrument, or they may use laser energy to break it up into small pieces so that it can be passed naturally in your urine.
Ureteroscopy is carried out under general anaesthetic (where you're unconscious), so you shouldn't drive or operate machinery for up to 48 hours after the procedure.
For stones up to 15mm (0.6in), a ureteroscopy is effective in 50-80% of cases.
A plastic tube called a stent may need to be temporarily inserted inside you to allow the stone fragments to drain into the bladder.
Percutaneous nephrolithotomy (PCNL)
PCNL is an alternative procedure that may be used for larger stones. It may also be used if ESWL isn't suitable – for example, because the person being treated is obese.
PCNL involves using a thin telescopic instrument called a nephroscope. A small incision is made in your back and the nephroscope is passed through it and into your kidney. The stone is either pulled out or broken into smaller pieces using a laser or pneumatic energy.
PCNL is always carried out under general anaesthetic, so you shouldn't drive or operate machinery for up to 48 hours after the procedure.
PCNL is 86% effective for stones that are 21-30mm (0.8-1.2in) in diameter.
Nowadays, open surgery for kidney stones is rare (less than 1% of cases require this type of surgery). It's only usually used if there's a very large stone or abnormal anatomy.
During open surgery, an incision will be made in your back so that your surgeon is able to access your ureter and kidney. The kidney stone can then be removed.
Treating uric acid stones
If you have a uric acid stone, you may be advised to drink around three litres (just over five pints) of water each day to try to dissolve it.
Uric acid stones are much softer than other types of kidney stone, and they can be made smaller if they're 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.
Complications of treatment
Complications can occur following the treatment of large kidney stones. Your surgeon should explain these to you before you have the procedure.
Possible complications will depend on the type of treatment you have and the size and position of your stones. Complications could include:
- sepsis – an infection that spreads through the blood, causing symptoms throughout the whole body
- a blocked ureter – caused by stone fragments; the ureter is the tube that attaches the kidney to the bladder
- an injury to the ureter
- a urinary tract infection
- bleeding during surgery
It's estimated that 5-9% of people may experience complications after having a ureteroscopy.
The best way of preventing kidney stones is to make sure you drink plenty of water each day to avoid becoming dehydrated.
Keeping your urine diluted helps to stop waste products getting too concentrated and forming stones.
You can tell how diluted your urine is by looking at its colour. The darker your urine is, the more concentrated it is.
Your urine is usually a dark yellow colour in the morning because it contains a build-up of waste products that your body has produced overnight.
Drinks such as tea, coffee and fruit juice can count towards your fluid intake, but water is the healthiest option and is best for preventing kidney stones developing.
You should also make sure you drink more when it's hot or when you're exercising, to replenish fluids lost through sweating.
Read more about preventing dehydration .
If your kidney stone is caused by too much calcium, you may be advised to reduce the amount of oxalates in your diet.
Oxalates prevent calcium being absorbed by your body, and can accumulate in your kidney to form a stone.
Foods that contain oxalates include:
- almonds, peanuts and cashew nuts
- soy products
- grains, such as oatmeal, wheat germ and wholewheat
Don't reduce the amount of calcium in your diet unless your doctor advises you to. This is because calcium is very important for maintaining healthy bones and teeth.
To avoid developing a uric acid stone, you should reduce the amount of meat, poultry and fish in your diet. You may also be prescribed medication to change the levels of acid or alkaline in your urine.
If you have a kidney stone, medication will usually be prescribed for pain relief or to prevent infections developing.
However, some medication may need to be reviewed by your doctor if it's thought to be causing your kidney stone.
The type of medication your doctor prescribes will depend on the type of kidney stone you have.
For example, if you have:
- calcium stones – you may be prescribed a diuretic medication if they are caused by hypercalcuria (an inherited condition)
- struvite stones – you may be prescribed antibiotics to help prevent a urinary tract infection or kidney infection , which are the main causes of struvite stones
- uric acid stones – you may be prescribed allopurinol (a medication used to lower uric acid levels) and medication to help alkalise your urine
- cystine stones – you may be prescribed medication to lower levels of cystine in your urine