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).

Causes of kidney stones

Kidney stones are usually formed following a build-up of certain chemicals in the body.

This build-up may be any of the following:

• calcium
• ammonia
• 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

Medication

There’s evidence to suggest that certain medications may increase your risk of developing recurrent kidney stones. These include:

• aspirin
• antacids
• diuretics (used to reduce fluid build-up)
• certain antibiotics
• certain antiretroviral medication (used to treat HIV)
• certain anti-epileptic medication

If you are in severe pain, your GP 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.

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 GP if it’s thought to be causing your kidney stone.

The type of medication your GP 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

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Types of kidney stones

Kidney stones can develop for a number of reasons.

Calcium stones

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

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
• chemotherapy

Cystine stones

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.

Diagnosing kidney stones

Your GP 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).

Imaging tests

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 to pass out on their own in your urine, and it's often possible to manage the symptoms at home with medication.

Larger stones may need to be broken up using ultrasound or laser energy. Occasionally, keyhole surgery is 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 get them again within the following 5 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 stop waste products forming into kidney stones.

Read more about preventing kidney stones.

Blocked ureter and kidney infection

A kidney stone that blocks the ureter can lead to a kidney infection. This happens because waste products can't get past the blockage, which may let bacteria build up.

The symptoms of a kidney infection are similar to the 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
• diarrhoea
• cloudy, bad smelling urine

Read more about kidney infections.

Treating kidney stones

Most kidney stones are small enough, less than 4mm across, to pass out in your urine, and can probably be treated at home.

But even small kidney stones can be painful, though this usually only lasts a couple of days and eases once the stone has passed.

Self care

You may be told to wait until you pass the stone naturally when you go to the toilet, and to try to catch it in your urine. You can do this by filtering your urine through gauze or a stocking.

Give the stone to your doctor so it can be analysed, which helps decide what further treatment, if any, you may need.

You should drink enough water to keep 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 is causing severe pain, your doctor may admit you to hospital for treatment.

This may be necessary if:

• you're at higher 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 pass naturally, around 6mm to 7mm (about 0.23in to 0.27in) across or larger, you may need treatment to remove it another way.

This could include:

• extracorporeal shock wave lithotripsy (ESWL)
• ureteroscopy
• percutaneous nephrolithotomy (PCNL)
• open surgery

The treatment you're offered 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 works by using ultrasound (high frequency sound waves) to pinpoint exactly where the stone is. Shock waves are then sent to the stone from a machine to break it into smaller pieces, small enough to be passed in your urine.

ESWL can be uncomfortable, so it's usually carried out after you've been given painkilling medication.

You may need more than one session of ESWL to fully treat your kidney stones. It's up to 99% effective for stones up to 20mm (0.8in) across.

Ureteroscopy

If a kidney stone is stuck in the ureter, you may need a ureteroscopy, sometimes also called retrograde intrarenal surgery (RIRS).

This 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 guided up into your ureter to where the stone is stuck.

The surgeon may gently remove the stone using another instrument, or use laser energy to break it into small pieces so it can pass 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 afterwards.

For stones up to 15mm (0.6in) across, ureteroscopy works in 50% to 80% of cases.

A small plastic tube called a stent may need to be placed temporarily to let the stone fragments drain into the bladder.

Percutaneous nephrolithotomy (PCNL)

PCNL is an alternative procedure used for larger stones. It may also be used if ESWL isn't suitable, for example if the person being treated is obese.

PCNL uses a thin telescopic instrument called a nephroscope. A small cut is made in your back, and the nephroscope is passed through it into your kidney. The stone is then either pulled out whole or broken into smaller pieces using laser or pneumatic energy.

PCNL always requires a general anaesthetic, so you shouldn't drive or operate machinery for up to 48 hours afterwards.

PCNL is 86% effective for stones between 21mm and 30mm (0.8in to 1.2in) across.

Open surgery

Open surgery for kidney stones is rare nowadays. Less than 1% of cases need this type of surgery. It's usually only used if there's a very large stone or unusual anatomy involved.

During open surgery, a cut is made in your back so the surgeon can reach your ureter and kidney, and the stone is removed directly.

Treating uric acid stones

If you have a uric acid stone, you may be advised to drink around 3 litres (just over 5 pints) of water each day to help dissolve it.

Uric acid stones are much softer than other types of kidney stone, and they can shrink when exposed to alkaline fluids.

You may also need medication to make your urine more alkaline before the stone starts to dissolve.

Complications of treatment

Complications can sometimes follow treatment for large kidney stones. Your surgeon should explain these to you before the procedure.

Possible complications depend on the type of treatment and the size and position of your stones, and could include:

• sepsis, an infection that spreads through the blood and causes symptoms throughout the body
• a blocked ureter, caused by stone fragments (the ureter is the tube connecting the kidney to the bladder)
• injury to the ureter
• a urinary tract infection
• bleeding during surgery
• pain

It's estimated that 5% to 9% of people may experience complications after a ureteroscopy.

The best way to prevent kidney stones is to drink plenty of water every day so your body doesn't become dehydrated.

Keeping your urine diluted stops waste products from becoming too concentrated and forming stones.

You can tell how diluted your urine is by its colour. The darker it is, the more concentrated it is.

Your urine is usually dark yellow in the morning, since it holds the waste your body has built up overnight.

Tea, coffee and fruit juice can all count towards your fluid intake, but water is the healthiest choice and works best for preventing kidney stones.

Drink more than usual when the weather is hot or when you're exercising, to make up for the fluid you lose through sweat.

Read more about preventing dehydration.

Diet

If your kidney stone is caused by too much calcium, your doctor may advise you to cut down on oxalates in your diet.

Oxalates stop calcium from being absorbed by your body, and they can build up in your kidney to form a stone.

Foods that contain oxalates include:

• beetroot
• asparagus
• rhubarb
• chocolate
• berries
• leeks
• parsley
• celery
• almonds, peanuts and cashew nuts
• soy products
• grains, such as oatmeal, wheat germ and wholewheat

Don't cut down on calcium in your diet unless your doctor tells you to, since calcium is essential for healthy bones and teeth.

To avoid developing a uric acid stone, cut down on meat, poultry and fish in your diet. You may also be prescribed medication to adjust the acid or alkaline levels in your urine.