Small, solid masses called kidney stones may form when salts or minerals, normally found in urine, become solid crystals inside the kidney. Normally, these crystals are too small to be noticed, and pass harmlessly out of your body. However, they can build up inside your kidney and form much larger stones.
If a stone becomes large enough, it may begin to move out of your kidney and progress through the ureter - a tube that carries urine from the kidney to your bladder. A kidney stone can become stuck at various parts of the ureter causing pain, infection and occasionally kidney damage.
Kidney stones shouldn't be confused with gallstones, which don't affect the kidneys and are caused by raised cholesterol levels.
Symptoms of kidney stones
Many kidney stones don't move and are too small to cause any symptoms. However, if a kidney stone causes a blockage, or moves into your ureter, you may:
have severe pain or ache on one or both sides of your back
get sudden spasms of excruciating pain - this usually starts in the back below your ribs, before radiating around your abdomen, and sometimes to your groin and genitals
have bloody or cloudy urine
feel sick or vomit
feel a frequent urge to urinate, or a burning sensation during urination
get fever and chills
You can also have these symptoms if you have a urinary tract infection (UTI) or cystitis. If you have one or more of these symptoms, you should ask your GP for advice.
The pain of kidney stones - referred to as 'renal colic' - can be very severe. It begins as soon as the stone becomes stuck in the 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 the body within a day or so and mostly within four weeks of the onset of symptoms. The bigger the stone the less likely it is to pass out of the body spontaneously. Stones greater than 5mm (a quarter of an inch) in diameter are the least likely to pass without medical help.
If you're pregnant and have any symptoms of kidney stones, see your GP straight away.
Complications of kidney stones
You may get damage to your kidneys and severe infection if you have a blockage so it's important that you visit your GP or attend hospital as soon as you can if you have any symptoms of kidney stones.
Causes of kidney stones
Men are four times more likely to get kidney stones than women, and if you have previously had a kidney stone then you will have a 50 percent chance of developing another one within five years. Most people have no predisposing factors to explain why they develop kidney stones. You may have an increased risk of developing kidney stones if you:
have a family history of kidney stones
are aged between 20 and 50
are taking certain medicines - for example indinavir (in the treatment of HIV infection) and taking too many laxatives or taking them too often
have only one kidney, or an abnormally shaped kidney
eat a diet high in protein
don't drink enough fluids
Diagnosis of kidney stones
Your GP will ask you about your symptoms and examine you. He or she may also ask you about your medical history. Your GP may do further tests to confirm the diagnosis and to show the size, location and type of your kidney stone. These include:
blood tests - to identify excess amounts of certain chemicals which cause kidney stones
urine analysis - to look for signs of infection
taking an X-ray image - stones that contain calcium usually show up white on X-ray images
intravenous urogram (IVU) - injection of a special dye that shows up the whole urinary system and any stones on X-ray images; or a CT (computed tomography) scan - this uses X-rays to make a three-dimensional image of the area
ultrasound scan - this uses high frequency sound waves to produce an image of the internal organs
Treatment of kidney stones
Your treatment will depend on the type and cause of your kidney stone. Most stones can be treated without surgery. If you drink a lot of water (two and a half to three litres per day) and stay physically active, this is often enough to remove stones smaller than about 5mm from your body. Your GP may then prescribe medicines to reduce the pain.
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.
If you have a kidney stone that hasn't passed out of the body within one to two months, it's unlikely to pass without treatment.
Non-surgical treatments
Infections are usually treated with antibiotics. If you have a blockage or a risk of kidney damage, your doctor will suggest treatment to remove your kidney stone.
Extracorporeal shock wave lithotripsy (ESWL)
This is the most common method of dealing with kidney stones. Your doctor will use X-ray imaging or ultrasound scanning to find your kidney stone. While you're lying down, a machine called a lithotriptor sends 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 a local anaesthetic.
After a local anaesthetic it may take several hours before the feeling comes back into the treated area.
Surgery
Ureteroscopic stone removal
If your stone is lodged in the ureter, your surgeon will pass a narrow, flexible instrument called a cystoscope up through your urethra and your bladder. Your urethra is the tube that carries urine from the bladder and out through the penis/vulva. A laser beam or shock waves generated by a device attached at the end of the cystoscope removes or breaks up the stone. This procedure is usually done under a general anaesthetic.
Percutaneous nephrolithotomy (PCNL)
Large stones can be surgically removed from the kidney. Your surgeon makes a small cut in your back and uses 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.
General anaesthesia temporarily affects your coordination and reasoning skills, so you must not drive, drink alcohol, operate machinery or sign legal documents for 48 hours afterwards. If you're in any doubt about driving, please contact your motor insurer so that you're aware of their recommendations, and always follow your doctor/surgeon's advice.
Prevention of kidney stones
You should increase the amount of water or weak cordial you drink to help prevent any type of kidney stone. You should aim to drink at least two litres every 24 hours, or at least enough to make your urine clear rather than a yellow colour. Talk to your GP for more advice on this. It's particularly important that you don't become dehydrated. Drink plenty of fluids in hot weather, when you travel or if you have a fever.
Some people develop very specific types of kidney stone that only come to light when they are analysed. These special types of stone may require specific prevention strategies. If you get calcium oxalate stones, for example, you should cut down on foods that have high levels of oxalate. These include chocolate, tea, rhubarb, spinach and strawberries.
If you get uric acid stones, you should eat less meat, fish and poultry, and your GP may prescribe medicines to help reduce levels of uric acid in your urine.
Your GP may prescribe medicines to reduce the chance of you getting cystine stones.
If you develop struvite (or infection) stones, you may need to take long-term antibiotics to keep your urine free of the bacteria that are causing the infection.
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