Kidney Stones

How common are kidney stones?

About 3 in 20 men, and 1 in 20 women in the UK develop a kidney stone at some stage in their life. It can occur at any age, but most commonly occurs between the ages of 20 and 40. About half of people who develop a kidney stone will have at least one recurrence at some stage in the future.

How do kidney stones form?

The kidneys filter the blood, and remove excess water and waste chemicals to produce urine. Urine travels from each kidney down a tube called the ureter into the bladder, then out of the body via the urethra when the bladder is full. Many waste chemicals are dissolved in the urine. The chemicals sometimes form tiny crystals in the urine which clump together to form a small stone.

What are the symptoms of kidney stones?

• Pain from a kidney. A stone that is stuck in a kidney may cause pain in the side of the abdomen.
• Renal colic. This is a severe pain caused by a stone that passes into the ureter (the tube that leads from the kidney to the bladder). The stone becomes stuck. The ureter 'squeezes' the stone towards the bladder which causes intense pain in the side of your abdomen. The pain may spread down into the lower abdomen or groin. You may sweat or feel sick due to the pain.
• Blood. You may see blood in your urine (urine turns red) caused by a stone 'rubbing' against the inside of your ureter.

What causes kidney stones?

Unknown cause
In most cases, there is no known reason why a stone forms. Most stones are made of calcium. However, in most cases, the amount of calcium and other chemicals in the urine is normal. You are more likely to form a stone if your urine is concentrated. For example, if you exercise vigorously, or if you live in a hot climate, or if you work in a hot environment when you may lose more fluid as sweat, and less as urine.

Underlying causes are uncommon
In a small number of cases, an uncommon medical condition is the cause. Various uncommon conditions can lead to high levels of chemicals in the body such as calcium, oxalate, uric acid, and cystine. If the level of these chemicals is high enough in the urine, they can form into stones.

Taking certain medicines can make you more prone to making kidney stones. These include: acetazolamide, allopurinol, antacids, aspirin, calcium and vitamin D supplements, steroids, indinavir, loop diuretics, nelfinavir, probenecid, quinolones, sulphonamides, theophylline, thiazides, triamterene, and high-dose vitamin C.

Note: although a lot of the above medicines are commonly prescribed, they do not commonly cause kidney stones. They are only the cause in a small number of cases. If you suspect that a medicine is the cause, then do not stop taking the medicine but discuss it with your doctor. A change of medication may be appropriate, but only after advice from your doctor.

You are also more prone to develop kidney stones if you have:

• recurrent urine or kidney infections.
• only one working kidney or have an abnormal kidney.
• close relatives who have had kidney stones.

Are any tests needed?

Tests to confirm the presence of a kidney stone
If you have symptoms that suggest a kidney stone, special x-rays or scans of the kidneys and ureters may be done. These tests aim to detect a stone and to check that a stone is not blocking the flow of urine.

Tests to rule out or confirm an underlying cause
Kidney stones are common and in most cases they are not caused by a known underlying disease. However, some routine tests may be advised to rule out underlying problems. In particular, tests are more likely to be advised if you have recurring kidney stones, or have symptoms of an underlying condition, or have a family history of a particular condition, or if a stone forms in a child or young person. Tests which may be advised include:

• A blood test to check that the kidneys are working properly.
• Blood tests to check the level of certain chemicals such as calcium and uric acid.
• Urine tests to check for infection and for certain crystals.
• An analysis of the stone if you pass it out. To catch a stone, pass urine through gauze, a nylon stocking, a tea strainer, or a filter such as a coffee filter.

If the pain eases with pain relief and you do not have symptoms to suggest complications (most cases), then your doctor may arrange the tests to be done as an out-patient. However, some people are admitted to hospital for pain relief and tests.

What are the possible complications from kidney stones?

Complications from kidney stones are uncommon (although the pain at the time can be severe). Sometimes a large stone can completely block the passage of urine down one ureter. This may lead to infection or damage to the kidney. This is usually avoided as x-ray tests will detect a blockage, and large stones can be removed.

What is the treatment for kidney stones?

The common situations
Most stones that cause renal colic are small, and pass out with the urine in a day or so. Drink plenty to encourage a good flow of urine. Strong painkillers are often needed to ease the pain until you pass the stone. (Some people are admitted to hospital for strong pain relief as the pain can be intense.) No other treatment is usually needed.

Some stones that form and stick in the kidney do not cause symptoms or any harm. They can just be left if they are small.

In some cases
Some stones become stuck in a ureter or kidney and cause persistent symptoms or problems. There are various treatment options which include the following:

• Extracorporeal shock wave lithotripsy (ESWL). This uses high energy 'shock waves' which are focussed onto the stones from a machine outside the body to break up stones. You then pass out the tiny broken fragments when you pass urine.
• Percutaneous nephrolithotomy (PCNL) is used for stones not suitable for ESWL. A nephroscope (a thin telescope-like instrument) is passed through the skin and into the kidney. The stone is broken up and the fragments are removed via the nephroscope. This procedure is usually done under general anaesthetic.
• Ureteroscopy is another treatment option that may be used. In this procedure, a thin telescope is passed up into the ureter via the urethra and bladder. Once the stone is seen, a laser (or other form of energy) is used to break up the stone. This technique is suitable for most types of stone.
• Stone removal can be done by a traditional operation where the skin has to be cut to allow access to the ureter and kidney. This is only needed in a very small number of cases where the above newer techniques have failed, or are not possible.

Another option for a stone made purely from uric acid (about 1 in 20 stones) is to dissolve the stone. This can be done by drinking plenty and making the urine alkaline with medication.

What can I do to help prevent a recurrence of a kidney stone?

About half of people who have a kidney stone develop another one within 10 years. Sometimes stones can be prevented from forming.

Have plenty to drink
If you have had one stone, you are less likely to have a recurrence if you drink plenty of fluid, mainly water, throughout the day (and night). The aim is to keep the urine dilute. (Your urine is more dilute if it is clear of colour rather than a yellow or green colour.) To do this, aim to drink at least three litres a day (unless your doctor advises otherwise if you have other medical problems). Have a large glass of water at bedtime, and also during the night if you wake to go to the toilet. If you work or live in a hot environment, you should drink even more.

Other advice
For the few people who have a high level of certain chemicals in the body, further specific advice may be given. For example:

• A dietitian may advise people with calcium oxalate stones to reduce the oxalate content of their diet.
• Uric acid stones can be prevented with a medicine.
• Other advice from a specialist may be appropriate for rarer conditions.

© EMIS and PIP 2005   Updated: September 2005   PRODIGY Validated