Icon - What are kidney stones

What are kidney stones

The kidneys filter the blood and remove the extra waste and water as urine. Many waste chemicals are in the urine. They can sometimes form crystals that clump together to make stones.

Kidney stones are hard, rock-like crystals of varying sizes and shapes. They can range from as small as a grain of sand to as big as a golf ball.

There are four main types of kidney stones:

  • The most common are those formed from calcium combined with oxalate or phosphate.
  • Struvite stones are caused by a urine infection and are often horn-shaped and quite large.
  • Uric acid stones are often softer than other forms of kidney stone.
  • Cystine stones are rare and hereditary and look more like crystals than stones.

Animated films help us understand how kidney stones form and why. Here you can view a short but informative animation produced by the National Health Service (UK).

Links to fact sheets and other helpful information can be found here: Resource Library.

Kidney stonesThe causes
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