The reason why most kidney stones form is not known. A stone may cause no problems but often it causes pain. Most kidney stones are small and pass out with the urine. Some stones become stuck in a kidney or in the tube draining urine from the kidney (the ureter). They can then cause persistent symptoms or problems. There are various treatment options to remove a stuck stone. About half of people who have a kidney stone develop another one at a later time in their life. Drinking plenty of water each day may prevent this from happening again (a recurrence).
What are kidney stones?
Kidney stones can form in the kidney, in the tube draining urine from the kidney (the ureter) or in the bladder. They can be many different sizes and shapes. The size of kidney stones ranges from tiny microscopic crystals to stones as large as potatoes.
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 lives. They can happen at any age but most commonly occur between the ages of 20 and 40. About half of people who develop a kidney stone will find it happens again (recurs) at least once at some stage.
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 the tube draining urine from the kidney (the ureter) into the bladder. It then travels 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?
In some cases, a kidney stone lies in a kidney and causes no problems or symptoms. You may not be aware that a stone has formed. If symptoms do occur, they include one or more of the following:
- 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 – which usually comes and goes but may sometimes also be constant – and is caused by a stone that passes into the tube draining urine from the kidney (the ureter). The stone becomes stuck. The ureter squeezes the stone towards the bladder, which causes intense pain in the side of your tummy (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.
- Infection. Urine infections are more common in people with kidney stones. Infections can cause high temperature (fever), pain on passing urine and increased frequency of passing urine.
What causes kidney stones?
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 and blood is normal. You are more likely to form a stone if your urine is concentrated. For example, if you exercise vigorously, 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, a 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.