​KIDNEY STONE DISEASE - BASICS

1. What do the kidneys do?

The kidneys are two bean-shaped organs that sit on either side of your spine, just under the ribs in your back. Their main jobs are:

• To filter waste products and extra fluid out of the blood

• To keep the balance of water and salts in the body

• To make some important hormones (for blood pressure and red blood cell production)

The liquid produced by this filtering process is called urine. Urine travels from the kidneys through thin tubes called ureters, down to the bladder, and then leaves the body through the urethra when you pass urine.

2. What is a kidney stone? How common is it?

A kidney stone is a hard lump that forms inside the kidney when minerals in the urine stick together and crystallise.

• About 1 in 10 people will have a kidney stone at some point in their life.

• It is most common between the ages of 30 and 60.

• It is slightly more common in men, but women are also affected.

Modern lifestyle plays a big role: not drinking enough water, sitting too much, eating a lot of processed food and salt, and being overweight all increase the risk of stones.

3. How do kidney stones form?

Your urine contains many dissolved substances such as calcium, oxalate and uric acid. Normally, these stay dissolved and are passed out in the urine without any problem. Stones tend to form when:

• You do not drink enough water (so there is less fluid but the same amount of minerals in the urine)

• There is a blockage or narrowing in the urinary tract, and urine cannot flow freely

• Some substances in the urine are higher than normal (for example, too much calcium in the urine, called hypercalciuria)

• You have repeated urine infections

When urine is too concentrated, these substances can come out of solution and form tiny crystals, like grains of sand. This is what people often call “passing gravel”. Over time, these crystals can stick together and grow into larger stones.

4. Types of kidney stones

The main types of kidney stone are:

• Calcium stones

  • The most common type.

  • Usually made of calcium oxalate or calcium phosphate.

  • High salt intake, certain metabolic problems, some medicines, high-dose vitamin D and family tendency can increase the risk.

• Uric acid stones

  • More likely in people who eat a lot of meat, who have gout or who have very acidic urine.

• Struvite stones (infection stones)

  • Usually related to repeated urine infections.

• Cystine stones

  • Rare.

  • Due to an inherited (genetic) problem that causes too much cystine to leak into the urine.