Kidney stones

About kidney stones

Kidney stones are common – five to 10 in 100 people are affected by pain associated with kidney stones at some point in their life. Most people who get kidney stones for the first time are aged between 20 and 50.

You normally have two kidneys, which ‘clean’ your blood, and filter out water and waste products to make urine. Kidney stones can form when there is an imbalance of salts or minerals in your urine. These minerals form into crystals, which are often too small to notice, and pass harmlessly out of your body. However, over time, they can build up inside your kidney to form a kidney stone.

Most kidney stones (about four out of five) are made up of calcium salts (calcium oxalate or calcium phosphate, or both). They can also be made up of other substances, including uric acid, cystine and struvite. They can range in size and may be smooth or jagged in texture.

Kidney stones can move out of your kidney into your ureter – the tube that carries urine from your kidney to your bladder. This can cause severe pain, known as renal colic.

Symptoms of kidney stones

Many kidney stones are too small to cause symptoms. But if a kidney stone causes a blockage or moves into your ureter, it may cause symptoms, such as:

  • severe pain or ache on one or both sides of your back
  • sudden spasms of excruciating pain – this usually starts in the back below your ribs, radiating around your abdomen, and sometimes to your groin and genitals
  • blood in your urine
  • feeling sick or vomiting
  • needing to urinate often, or feeling a burning sensation during urination

The pain of kidney stones – called renal colic – can be very severe. It begins as soon as the stone becomes stuck in your ureter and tends to come in waves. It's not usually associated with the size of the kidney stone – sometimes small stones can cause more pain than very large ones.

Small kidney stones are usually passed out of your body within a day or so and mostly within six weeks. Bigger stones are less likely to pass out of your body spontaneously. Stones greater than 5mm (a quarter of an inch) in diameter are the least likely to pass without medical help.

If you have any symptoms of kidney stones, you should see your GP. If your symptoms are severe, you may need to seek urgent medical attention.

Complications of kidney stones

If the kidney stone completely blocks your ureter, it can stop the flow of urine. Without treatment to remove the kidney stone, this can lead to permanent damage to your kidneys within a number of weeks.

If a kidney stone is blocking your ureter, this can also cause severe infection, which can become life-threatening without treatment. Signs of an infection include having a fever and cloudy urine. It's important that you seek urgent medical attention if you have these symptoms.

Causes of kidney stones

Men are more likely to get kidney stones than women. About half of people who have had a kidney stone go on to get more within 10 years.

In most people, there is no obvious reason for what causes kidney stones, although you may be more likely to get them if you:

  • have a family history of kidney stones
  • are aged between 30 and 50
  • are taking certain medicines – for example, protease inhibitors (such as indinavir) and certain diuretics (such as triamterene)
  • are taking too many vitamin C or calcium/vitamin D supplements, or antacids
  • have a condition affecting the shape or structure of your kidney
  • have a lot of salt or protein in your diet
  • don't drink enough fluids
  • have certain conditions, such as hyperparathyroidism, high blood pressure or Crohn’s disease
  • have cystitis – the bacteria that cause this infection can break down the a substance found in urine called urea, which can lead to kidney stones

Diagnosis of kidney stones

Your GP will ask you about your symptoms and examine you. He or she may test a sample of your urine using a ‘dipstick’ to check for signs of infection and may send the sample to a laboratory for further tests.

Your GP may do more tests to confirm the diagnosis and/or refer you to a urologist (a doctor who specialises in identifying and treating conditions that affect the urinary system) for tests. These will show the size, location and type of kidney stone you have. You may have the following tests.

  • A full blood count – this is to check for signs of infection, to check how well your kidneys are functioning, and to check the levels of certain minerals that cause kidney stones.
  • CT (computed tomography) scan (may be referred to as a CT urogram) – this uses X-rays to make a three-dimensional image of your kidneys and urinary system.
  • Intravenous urogram (IVU) – this involves injection of a special dye that shows up the urinary system and any stones on X-ray images. You may be offered an IVU if CT urogram isn’t available in your hospital.
  • Ultrasound scan – this uses sound waves to produce an image of your kidneys and urinary system.
  • X-ray – stones that contain calcium usually show up white on X-ray images.
  • 24-hour urine collection – to check levels of certain minerals such uric acid, oxalate, phosphate and calcium in your urine.

Treatment of kidney stones

Your treatment depends on the type and cause of your kidney stone. Most stones can be treated without surgery.

Home treatment

Your GP may recommend home treatment. If your stone is smaller than about 5mm you can normally pass it in your urine. However, you may need some pain relief, and your GP will usually offer you medicines to reduce pain and sickness. See our frequently asked question for more information on pain relief. He or she may also advise you to make sure you drink enough fluids to help flush out the kidney stone.

Your GP may ask you to catch the kidney stone by passing your urine through filter paper or a tea strainer. The stone can then be analysed to find out what type it is, to help guide your treatment and prevent more stones.

If the kidney stone doesn’t pass out of your body within about six weeks, or your symptoms get worse, it's likely that you will need hospital treatment.

Medicines

If your urologist thinks you have an infection then he or she will prescribe you antibiotics.

If your kidney stone is less than 10mm (1cm) and doesn’t need to be removed immediately, your urologist may offer medicines called alpha-blockers to help the stone pass out in your urine. This is called medical expulsive therapy (MET). This treatment isn’t commonly used in the UK at present, however there is ongoing research to assess how well it works.

Non-surgical treatments

If your kidney stone can't pass out in your urine by itself, your urologist may advise you to have a procedure called extracorporeal shock wave lithotripsy (ESWL). In this procedure, your doctor will use a machine called a lithotripter to send shock waves through the skin of your abdomen (tummy) to your kidney stone to break it up into crystals small enough to be passed in your urine. You may feel some pain as the stone breaks up, so the procedure is usually performed under sedation with a painkiller.

You may need to have this procedure more than once to completely get rid of your kidney stones. ESWL may not be suitable if you are pregnant.

Surgery

If your kidney stone is very large, or is blocking your ureter and can’t be removed with ESWL, you may need keyhole surgery to remove it. Types of keyhole surgery include the following.

Ureteroscopic stone removal

This type of surgery can remove stones that are lodged in your ureter. Your surgeon will pass a narrow, flexible instrument called a ureteroscope up through your urethra, your bladder and ureter. A laser beam or shock waves from a device on the ureteroscope remove or break up the stone. Occasionally, if your surgeon is unable to pass the ureteroscope into your urethra, he or she may insert a soft tube (stent) first. This can help to relieve the obstruction and make it easier to insert the ureteroscope at a later date.

A soft tube (stent) may be left in your ureter for a few days until it heals. Ureteroscopy is usually done under general anaesthesia. This means you will be asleep during the procedure. If you have had a stent, you will be given a date to have it removed before you are discharged. Stents are usually removed under local anaesthesia.

Percutaneous nephrolithotomy (PCNL)

This is a type of surgery that can be used to remove large stones from your kidney. Your surgeon will make a small cut in your back and use a telescopic instrument called a nephroscope to pull the stone out or break it up using a laser beam or shock waves. PCNL is performed under general anaesthesia.

Prevention of kidney stones

If you have had a kidney stone, your doctor will probably advise you to increase the amount of water you drink, to prevent getting another one. Aim for enough to make your urine clear rather than yellow.

In addition, if you have had a calcium stone, your doctor may advise you to do the following.

  • Don’t eat more than 3g of salt a day – don’t add it to your food and avoid processed foods.
  • Cut down on foods that have high levels of oxalate – such as chocolate, tea, rhubarb, spinach, nuts and strawberries.
  • Eat less meat, fish and poultry – liver, kidneys, herrings with skin, sardines, anchovies and poultry skin increase the amount of uric acid in your urine.
  • Don’t take supplements containing calcium, vitamins A, C or D.

If you get uric acid stones, your GP may also prescribe medicines (such as allopurinol) to help reduce levels of uric acid in your urine.

I have been told that kidney stones are caused by drinking too much milk and eating too many foods that contain calcium. Is that true?

Answer

No, it isn't true. In fact, not eating enough calcium can make you more likely to develop a kidney stone. It's important to eat a healthy diet that contains calcium-rich foods.

Explanation

Four out of five kidney stones are made from calcium – either calcium oxalate or calcium phosphate. Because the stones are made from calcium, many people in the past thought that having too much calcium in your diet made kidney stones more likely. However, the opposite seems to be true – not eating enough calcium makes developing a stone more likely.

To stay healthy, it's important to eat a healthy, balanced diet that contains calcium. Foods rich in calcium include milk, cheese and other dairy products, leafy green vegetables and bony fish like sardines and pilchards. However, don't take calcium supplements unless your GP or urologist advises you to. Taking calcium supplements may actually increase your chances of developing a kidney stone.

If you have calcium kidney stones, your GP or urologist may advise you to cut out foods that contain high amounts of calcium oxalate. These include chocolate, spinach, nuts and rhubarb.

Speak to your GP, urologist or dietitian for advice before making any major changes to your diet.

How can I control the pain when passing a kidney stone?

Answer

Kidney stones can be very painful. Depending on how severe your pain is, there are a number of different painkillers that your urologist can prescribe for you.

Explanation

The pain you get with a kidney stone can become severe, usually when the stone moves from your kidney into the ureter – the tube that carries urine from your kidney to your bladder. The pain often starts suddenly, usually in your lower back, sometimes spreading to your groin.

If your kidney stone is smaller than 5mm, and you’re not in severe pain, your GP may recommend you stay at home and wait for the kidney stone to pass naturally.

Your GP will usually prescribe you a non-steroidal anti-inflammatory drug (NSAID), such as naproxen, to help you manage the pain at home. You may be given tablets to take by mouth or suppositories to be inserted into your rectum (back passage). Always read the patient information leaflet that comes with your medicine and if you have any questions, ask your GP or pharmacist for advice.

If the tablets or suppositories don’t help manage your pain, your GP may offer you an injection of painkiller, which can be combined with an anti-sickness medicine if you need it.

If NSAIDs aren't suitable for you or don't help to manage you pain, your urologist may offer you stronger painkillers, such as diamorphine or pethidine. Talk to your urologist for more information.

Will a kidney stone harm my health?

Answer

Most kidney stones pass easily in your urine and don't cause serious problems. However, if a kidney stone blocks your ureter (the tube which joins your kidney to your bladder) and it's not treated quickly, your kidney can become damaged or you may develop an infection. This can be life-threatening, which is why it's vital to get treatment quickly.

Explanation

Most kidney stones are small enough to be passed in your urine without needing any treatment and, apart from pain and discomfort, they don't cause any serious problems. Others may be painful but can be effectively treated and either broken up or removed. However, if the stone is large or gets stuck inside your ureter, it can cause more serious problems and will need to be treated.

If the stone blocks your ureter, urine can't flow down to your bladder and it collects in your kidney. This can cause your kidney to swell and if this isn't treated, it can cause permanent damage. If they aren't treated, kidney stones can also cause an infection which can spread and may become life-threatening.

You should seek urgent medical attention if you have signs of an infection, such as having a fever and cloudy urine.

Does having a kidney stone make me more likely to have another one?

Answer

Once you have had a kidney stone you're more likely to get another, compared to someone who has never had one. You can reduce your risk of having another kidney stone by making sure you drink enough fluids every day and making changes to your diet if necessary.

Explanation

Around one in seven people who have a kidney stone go on to develop another one within a year. One in three people develop another kidney stone within five years of the previous one. However, there are some things that you can do that will help to reduce your risk of developing another stone. By drinking enough fluids you can help to keep your urine watered down, which helps to prevent a build up of some of the minerals that can cause kidney stones. You're aiming for your urine to be clear, rather than a yellow colour.

Eat a healthy balanced diet, without too much salt or animal protein, such as meat and fish. If your previous kidney stone was caused by certain minerals, your GP or urologist may ask you to change the foods you eat. This can help to cut down the amount of these substances in your body and reduce your risk of having another kidney stone. Don't change your diet without advice from your GP, urologist or a dietitian.

Depending on the kind of stone you have had, and what caused it, you may need to take medicines that help to prevent another stone forming.