Kidney stones 

Kidney stones are stone-like lumps that can develop in one or both of the kidneys. The medical name for stones in the kidneys is nephrolithiasis. If the stones cause severe pain, this is known as renal colic. 

The kidneys 

The kidneys are two bean-shaped organs that are roughly four inches in length. They are located towards the back of the abdomen (stomach) on either side of the spine.

The kidneys remove waste products from the blood and transfer them into the ureter, along with excess fluids. The ureter is the tube that attaches each kidney to the bladder. From there, the waste products and excess fluid are disposed of as urine. The clean blood is then transferred back into the body.

Kidney stones

The waste products in the kidneys can occasionally form crystals that collect around the inside of the kidney. Over time, the crystals may build up to form a hard stone-like lump. This is a kidney stone.

There are four main types of kidney stone. See Kidney stones - symptoms for more information about the different types of kidney stones.

How common are kidney stones?

Kidney stones are quite common and usually affect people who are between 30 and 60 years of age. They affect men more than women. It is estimated that renal colic (severe pain caused by a kidney stone) affects about 10-20% of men, and 3-5% of women. 

Outlook 

After a kidney stone has formed, your body will try to pass it in urine, so it will often travel through the urinary system. The urinary system produces, stores and removes urine. The urinary system is made up of the kidneys, the ureters, the bladder and the urethra (the tube that carries urine from the bladder to the outside of the body).

While small stones may be passed out in the urine, it is fairly common for a stone to block part of the urinary system, such as the ureter or the urethra. If this happens, it can cause severe pain in the abdomen or groin. A blockage in the urinary system can also lead to:

• infection
• kidney damage
• kidney failure 

There are several procedures to remove, or break down, larger kidney stones. Around half of people who have had kidney stones will experience them again within the following 10 years.