Kidney stones
What are kidney stones?
Kidney stones are hard crystalline masses of varying shapes and sizes that form on the inside surface of the kidney. They are usually composed of calcium, phosphate or uric acid and vary in size from 2 mm across to 12 mm across.
How do they form?
Kidney stones form when certain substances in a person's urine become too concentrated. This results in minerals and other substances in their urine crystallizing out onto the inner surfaces of the kidney. The crystals can combine to form hard stones. Normally, urine contains chemicals that inhibit the crystals from forming.
How would I know if I had a kidney stone?
You may have kidney stones and not know about it. Most small kidney stones pass via the ureters (the tubes linking the kidneys and bladder) into the bladder without causing any problems. However, if you pass a large kidney stone, you will know about it, because you will be in pain, often excruciating pain.
Other symptoms of kidney stones are:
- blood in the urine;
- nausea and vomiting;
- an urgent feeling of needing to urinate;
- shivers and fever; and
- passing small stones in the urine (gravel).
When a stone starts to move into the urinary tract, a person may experience ‘renal colic’, which is an intense pain in the back, just below the ribs. The pain commonly radiates down into the groin — and the testicle in men.
Who is affected by kidney stones?
Men tend to get kidney stones 3 times as often as women. The peak incidence of kidney stones is between the ages of 20 to 40 years, but people of any age can be affected.
People who have had recurrent urine infections and people who have a family history of kidney stones are more susceptible to developing them, as are people with gout.
Prevention of stones
In order to avoid kidney stones, you need to drink plenty of water. People who have previously had a stone need to drink about 3 litres of water a day. Some types of kidney stone can be avoided by restricting particular foods.
Are there tests to detect kidney stones?
A plain X-ray of the abdomen can identify the majority of stones, showing their size and location in the urinary system.
An intravenous pyelogram (IVP) is a test where dye is used to highlight the kidneys on an X-ray. An IVP can identify any obstruction to the flow of urine that may be associated with a stone lodged in the urinary system, but requires the use of injected contrast dye (which can have side effects).
The spiral CT scan is a quick investigation that does not require any contrast dye. The CT machine rotates around the body to take pictures, and shows all types of kidney stones. An ultrasound of your abdomen can also be useful in diagnosing kidney stones.
X-rays may also be required to assess what type of kidney stone a person has, to determine whether the stone can be treated by shockwave therapy. Your doctor may also suggest a blood test to look for excess calcium or uric acid, or urine tests to see if you are over-excreting minerals, or have a lack of the chemicals that inhibit crystal formation. Analysing the stone itself (once it has passed or been removed) can also provide useful information to help prevent future stones from forming.
What is the treatment?
Some stones can be passed naturally through the urinary tract if the person drinks lots of water. Medical treatments used include stents (devices inserted into the urinary tract to open up the ureter for easier removal of stones), and stone fragmentation using lithotripters or lasers. ESWL (extracorporeal shockwave lithotripsy) uses shockwaves to shatter the stone, which can then pass as small fragments in the urine.
Some stones can be directly removed from the ureter by a ureteroscope, a fine instrument inserted into the ureter via the bladder. Fewer than one in a hundred people with kidney stones will need to have open surgery.
Last Reviewed: 15 August 2008
