Kidney stones (or calculi) are hard stones that can form in one or both of your kidneys. They can cause severe pain, known as renal colic.
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.
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:
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.
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.
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:
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.
Your treatment depends on the type and cause of your kidney stone. Most stones can be treated without surgery.
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.
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.
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.
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.
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.
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.
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.
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.
Produced by Pippa Coulter, Bupa Health Information Team, February 2013.
For answers to frequently asked questions on this topic, see FAQs.
For sources and links to further information, see Resources.
This information was published by Bupa's Health Information Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals. Photos are only for illustrative purposes and do not reflect every presentation of a condition. The content is intended only for general information and does not replace the need for personal advice from a qualified health professional. For more details on how we produce our content and its sources, visit the about our health information page.
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