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What are Kidney Stones?

Stones form in little crevices in the kidney. They can then fall out into larger passages in the kidney and then travel down the tube (ureter) towards the bladder. They usually take many years to form and for most of their life they are silent. Once stones have passed into the bladder they normally pass out very soon.

How common are urinary stones?

In the UK about 1 in 10 men and 1 in 20 women have a symptomatic episode from a stone. About half of these people will have another episode some time in the next 10 years. It is very uncommon for patients to have repeated trouble.

Why do stones matter?

Stones can cause severe pain which requires admission to hospital. Of more concern is the damage that they can cause to kidneys partly by blocking the urine drainage from the kidney but also by encouraging infections. 


What types of stones are there and what causes them?

Calcium oxalate

About 70% of stones are made from calcium oxalate. They have a very crystalline spiky surface and are extremely hard. In almost all patients we do not know why these stones form. In a minority there are abnormalities of calcium metabolism and your doctor will always check the level of calcium in your blood. Occasionally they look at the amount that passes out in the urine. 

Calcium phosphate

Again, it is unknown why these stones form. They have a smoother surface than oxalate stones and are slightly less hard. 

Calcium magnesium ammonium phosphate

These stones are associated with uncommon types of urinary infection – not the usual germ of E.Coli. The stones may be large and may form a complete cast of the urine collecting passages within the kidney – the shape that forms is likened to a stag horn.

Uric acid

These are uncommon stones – only about 10%. They are hard and very smooth. Uric acid is a breakdown product of cells particularly meat in the diet. They can sometimes be caused by gout – typically patients tend to be rather overweight, have a higher chance of being diabetic and may drink less fluid than others.


This is a very rare stone, only about 1% and is due to a genetic defect which allows a chemical called Cystine to leak out into the urine. This forms very hard stones which often begin in teenage years so patients are very much more likely to have repeated attacks throughout their lives.