Kidney stones

Kidney stones can form in one or both kidneys, and they most often affect people aged 30 to 60. They're quite common. Around 3 in 20 men and up to 2 in 20 women will get them at some stage of their lives.

The medical term for kidney stones is nephrolithiasis. If they cause severe pain, that pain is known as renal colic.

Small kidney stones can go unnoticed and pass out in the urine without any pain. 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 it causes a urinary tract infection (UTI).

Read more about the symptoms of kidney stones.

Waste products in the blood can sometimes form crystals, and these collect inside the kidneys. Over time the crystals may build up into a hard, stone-like lump. That lump is a kidney stone.

You are more likely to get one if you don't drink enough fluids, if you're taking some types of medicine, or if you have a medical condition that raises the levels of certain substances in your urine.

Once a kidney stone has formed, your body tries to pass it out in the urine when you go to the toilet. So the stone will often travel through the urinary system, which is made up of the kidneys, the kidney tubes and the bladder.

Most kidney stones are small enough to pass out of your body in your urine, and you may be able to treat the symptoms at home with medicine.

Larger stones may need to be broken up using ultrasound or laser energy. Occasionally, very large stones have to be removed directly with keyhole surgery.

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 them, drink plenty of water every day so you don't become dehydrated. It's very important to keep your urine diluted (clear), because that stops waste products forming into stones.

Read more about preventing kidney stones.

Very small kidney stones are unlikely to cause many symptoms. A small stone may even go unnoticed and pass out painlessly when you urinate.

Symptoms usually start if a kidney stone:

• gets stuck in your kidney
• starts to travel down the ureter (the tube that attaches each kidney to the bladder), which is narrow, so the stone can cause pain as it tries to pass through
• causes an infection

When this happens, kidney stones can cause these symptoms:

• 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), which may be caused by the stone scratching the kidney or ureter

A kidney stone can block the ureter, and when that happens you may develop a kidney infection. Waste products can't get past the blockage, so bacteria may build up.

The symptoms of a kidney infection are similar to those of kidney stones, but they may also include:

• a high temperature (fever) of 38C (100.4F) or over
• chills and shivering
• feeling very weak or tired
• diarrhoea
• cloudy and bad-smelling urine

Kidney stones usually form when certain chemicals build up in the body. The build-up may be of any of these:

• calcium
• ammonia
• uric acid (a waste product made when the body breaks down food to use as energy)
• cysteine (an amino acid that helps to build protein)

Some medical conditions can push the level of these substances in your urine unusually high. You're also more likely to get kidney stones if you don't drink enough fluids.

Some people are more likely than others to keep getting kidney stones. This includes people who:

• eat a diet high in protein and low in fibre
• 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

Some medicines may raise your risk of getting kidney stones again and again. The evidence points to these:

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

Calcium stones are the most common type of kidney stone. They form when there's too much calcium in the urine, and this can happen for a few reasons:

• 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. They most commonly form after a urinary tract infection that has lasted a long time. Women get them more often than men do.

Uric acid stones can form when there's a large amount of acid in your urine. A few things can cause this:

• 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 are the rarest type of kidney stone. They're caused by cystinuria, a condition you inherit from your parents, which affects the amount of acid that passes into your urine.

Your doctor can usually diagnose kidney stones from your symptoms and your medical history. It's particularly easy if you've had kidney stones before.

You may be given some 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 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 stone to analyse makes the diagnosis easier, and it may help your doctor decide which treatment will benefit you most.

If you have severe pain that painkillers don't control, 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 your doctor sends you to hospital for an imaging test with suspected kidney stones, a few different techniques may be used. These tests can help confirm the diagnosis, or show exactly where a kidney stone is.

The tests include:

• a computerised tomography (CT) scan, where a series of X-rays are taken at slightly different angles and a computer puts the images together
• X-ray, an imaging technique that uses high-energy radiation to highlight abnormalities in body tissue
• an ultrasound scan, which uses high-frequency sound waves to create an image of the inside of your body
• an intravenous urogram (IVU) or intravenous pyelogram (IVP), where a dye that shows up on X-ray is injected into a vein in your arm, and 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 test you have may depend on what's available at your local hospital.

Most kidney stones are small, less than 4mm in diameter, so they can pass out of your body in your urine. These stones can probably be treated at home.

Even a small kidney stone can be painful, though the pain usually lasts only a couple of days and goes away once the stone has passed.

If you're in severe pain with kidney stones, your doctor can give you pain relief by injection. If the pain hasn't eased after half an hour, a second dose can be given.

Medicine can also be injected to treat nausea (feeling sick) and vomiting. This is called an anti-emetic (anti-sickness) medicine.

You may also get a prescription for painkillers, anti-emetics, or both, to take at home.

Your doctor may advise you to wait until the kidney stone passes when you go to the toilet, and to try to catch it from your urine. You can do this by pouring your urine through gauze or a stocking.

Give the stone to your doctor, who can have it analysed. This helps decide what further treatment you may need.

Drink enough water to make your urine colourless. If your urine is yellow or brown, you're not drinking enough.

If a 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 send 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 medicine
• you're dehydrated and vomiting too much to keep fluids down
• you're pregnant
• you're over 60 years of age

A kidney stone that is 6mm to 7mm (about 0.23in to 0.27in) across or larger is usually too big to pass on its own. If that's the case, you may need treatment to remove it another way.

This could include:

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

Which treatment you have will depend on the size and location of your stones.

ESWL, short for extracorporeal shock wave lithotripsy, is the most common way of treating kidney stones that can't be passed in the urine.

The doctor uses ultrasound (high-frequency sound waves) to find exactly where the kidney stone sits. A machine then sends ultrasound shock waves to the stone and breaks it into smaller pieces, so you can pass them in your urine.

The treatment can be uncomfortable, so you'll usually be given painkilling medicine first.

You may need more than one session of ESWL to clear your kidney stones. It is up to 99% effective for stones up to 20mm (0.8in) in diameter.

If a kidney stone gets stuck in the ureter, you may need a procedure called ureteroscopy. Some doctors also call it retrograde intrarenal surgery (RIRS).

The surgeon passes 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. From there it goes up into your ureter, to the spot where the stone is stuck.

The surgeon may try to gently remove the stone with another instrument. Or they may use laser energy to break it into small pieces, so that you can pass them naturally in your urine.

Ureteroscopy is done 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), ureteroscopy works in 50% to 80% of cases.

A plastic tube called a stent may need to be put inside you for a while, to let the stone fragments drain into the bladder.

Percutaneous nephrolithotomy, or PCNL, is another way to treat kidney stones. Doctors may use it for larger stones. They may also choose it if ESWL isn't suitable, for example because the person being treated is obese.

PCNL uses a thin telescopic instrument called a nephroscope. The doctor makes a small incision in your back and passes the nephroscope through it into your kidney. The stone is then either pulled out or broken into smaller pieces using a laser or pneumatic energy.

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

For stones that are 21mm to 30mm (0.8in to 1.2in) in diameter, PCNL is 86% effective.

Open surgery for kidney stones is rare these days. Fewer than 1% of cases need it. Doctors usually keep it for a very large stone or for abnormal anatomy.

In open surgery, the surgeon makes a cut (an incision) in your back so they can reach your ureter and kidney. The kidney stone can then be removed.

If you have a uric acid stone, your doctor may advise you to drink around 3 litres (just over 5 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 become smaller when they're exposed to alkaline fluids.

You may also need to take some medicine to make your urine more alkaline before the uric acid stone starts to dissolve.

Complications can happen after treatment for large kidney stones. Your surgeon should explain them to you before the procedure.

Which complications you might face depends on the type of treatment you have, and on the size and position of your stones. They could include:

• sepsis, an infection that spreads through the blood and causes 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
• pain

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

The best way to prevent kidney stones is to drink plenty of water every day, so you don't become dehydrated. When your urine stays diluted, waste products can't become too concentrated and form stones.

You can judge how diluted your urine is by its colour. The darker it is, the more concentrated it is. In the morning it's usually dark yellow, because waste products your body made overnight have built up.

Tea, coffee and fruit juice all count towards your fluid intake. Water is still the healthiest choice, though, and the best one for preventing kidney stones from developing.

Drink more when the weather is hot or when you're exercising, to replace the fluids you lose through sweating.

If your kidney stone is caused by too much calcium, your doctor may advise you to cut down on oxalates in your food. Oxalates stop your body absorbing calcium, and they can build up in the kidney and 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 the calcium in your diet unless your doctor tells you to. Calcium is very important for keeping your bones and teeth healthy.

To avoid a uric acid stone, you should eat less meat, poultry and fish. You may also be prescribed medicine to change the acid or alkaline levels in your urine.

If you have a kidney stone, you'll usually be given medicine for pain relief, or to stop infections developing.

Sometimes your doctor may need to review a medicine you already take, if it's thought to be causing your kidney stone.

The medicine your doctor prescribes depends on the type of stone you have. For example, if you have:

• calcium stones: you may be prescribed a diuretic medicine 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 medicine used to lower uric acid levels) and medicine to help alkalise your urine
• cystine stones: you may be prescribed medicine to lower levels of cystine in your urine