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A kidney stone, also known as a renal calculus, is a solid crystal build-up formed in the kidneys from dietary minerals in the urine. Stones can occur within the kidney itself as well as in the ureter (the tube draining urine from the kidney) or in the bladder. Sizes can vary, ranging from tiny microscopic crystals to stones as large as golf balls.
Kidneys filter the blood by removing excess water and waste chemicals to produce urine. Urine passes from each kidney down a tube called the ureter into the bladder, then out of the body via the urethra once the bladder becomes full. Many waste chemicals are dissolved in the urine and these chemicals sometimes form small crystals in the urine which clump together to form a stone.
In the UK, about 15% of men and 5% of women will develop a kidney stone at some stage in their life. They can occur at any age but most commonly occur in people aged between 20 and 40. Roughly half of all people who develop a kidney stone will have a recurrence again in the future.
In some cases it is possible for a kidney stone to sit in a kidney without causing a problem. You may be unaware that a stone has formed, though If symptoms do occur, they include one or more of the following:
In most cases, the reason for a stone forming is not always known. The majority of stones are made of calcium, though in most cases, the levels of calcium and other chemicals in the urine and blood is normal. Stones are more likely to form if your urine is concentrated. For example, you may be at risk if you exercise vigorously or if you live or work in a hot environment where you may lose more fluid as sweat and less as urine.
In a small number of cases, a medical condition is the cause. Some uncommon conditions can lead to higher than normal levels of chemicals in the body, such as calcium, oxalate, uric acid and cystine. If the level of these chemicals is high enough, they can form stones.
Certain medicines can make you more prone to developing kidney stones. These include diuretics (water tablets), some chemotherapy drugs used in the treatment of cancer and some drugs used to treat HIV. However, many people safely take these medicines without ever developing a kidney stone. If you suspect that the medication you are taking is causing your kidney stone, you should always consult with your doctor. Do not stop taking your medication without seeking medical advice.
You are also more prone to develop kidney stones if you have:
If you have symptoms that suggest a kidney stone, a scan or X-ray of the kidneys and ureters may be done. The aim of these tests is to detect a stone and to check whether or not it is blocking the flow of urine.
Kidney stones are common and in most cases they are not caused by a known underlying condition. However, Some routine tests are available to rule out any underlying problems. Tests are more likely to be advised if you have symptoms of an underlying condition, suffer from recurring kidney stones, have a family history of a particular condition or if a stone forms in a child or adolescent. Tests which may be advised include:
Although the pain of kidney stones can be severe, complications are uncommon. Sometimes a large stone can completely block the passage of urine down one ureter and this may lead to infection or damage to the kidney. This can usually be avoided, as blockages can be detected by X-rays or scans and large stones can be removed.
Most stones that cause renal colic are small and can be pass out with the urine in a day or so. Drink plenty of water to encourage a good flow of urine. Your Doctor may prescribe strong painkillers to ease the pain until you pass the stone. Often no other treatment is needed. Some stones that form and stick in the kidney do not cause symptoms or any harm and can be left if they are small. Sometimes you may be offered medication to help the stone pass through.
Sometimes stones become stuck in a ureter or kidney and can cause persistent problems. In these cases, the pain may become quite severe and you may need to be admitted to hospital. There are various treatment options which include:
In this video one of our kidney stones specialists Mr Leye Ajayi performs kidney stone removal surgery. Please note, this video contains footage from the operation.
About half of all people who have a kidney stone develop another one within 10 years. Sometimes stones can be prevented from forming.
If you have had one stone, you are less likely to have a recurrence if you drink plenty of water throughout the day. By keeping urine diluted you reduce the chance of chemical build up. You should aim to drink between two and three litres a day (unless your doctor advises otherwise). If you live or work in a hot environment, you should drink even more.
For the few people who have a high level of certain chemicals in the body, further specific advice may be given. For example: