Causes

It is not normal to form a kidney stone. Formation of a stone implies there is something abnormal in the urinary system. There are always many chemicals in everybody’s urine and in most people these chemicals are dissolved in the urine. In other words, the chemicals are not solid.

When there is a chemical or physical abnormality in the kidneys, the chemicals may precipitate (become solid particles). These particles can become tiny crystals which eventually grow to become a kidney stone.

Why do kidney stones form?

Every person’s urine contains chemicals that are normally excreted from the body. Each person is unique and just as each person’s body chemistry is different, each person’s urine chemistry is also different. These variations are largely due to genetic differences between individuals rather than representing a disease process. In some patients the particular chemical makeup and concentration of their urine predisposes them to stone formation by precipitation of tiny crystals which may grow into kidney stones.

In some people it is an excess of a chemical which predisposes them to forming stones e.g. too much calcium or oxalate in the urine. In other individuals it is the lack of a chemical which normally stops stones forming which is the problem e.g. patients with low levels of citrate in the urine are more likely to produce kidney stones.

It is important to understand that these chemical variations in urine are not usually related to dietary intake but are simply a reflection of genetic variation. This does not mean that the predisposition is always inherited as may patients with stone disease do not have a family history of stone disease.

What are kidney stones made of?

Most kidney stones in Australia are Calcium stones, either Calcium Oxalate or Calcium Phosphate. Calcium stones account for over 90% of stones and are usually idiopathic – not caused by a specific disease process. Calcium stones are hard (like a rock) and cannot be dissolved. The composition of kidney stones generally does NOT relate to dietary intake.

Composition of Kidney Stones

  • Calcium Stones
    • Calcium Oxalate
    • Calcium Phosphate
    • Mixed Calcium Oxalate / Calcium Phosphate
  • Uric Acid Stones – usually a genetic predisposition
  • Struvite Stones – from recurrent Urinary Tract Infections
  • Cystine Stones – rarely seen, associated with a genetic disease
  • Xanthine Stones – very rare
  • Stones caused by medicines (very rare) e.g. indinavirsulfadiazine and triamterene.

Causes of Renal Stone Disease

There are a wide range of causes of Renal Stone Disease:

  • Idiopathic.
  • Hypercalcaemia.
  • Uric acid pathology.
  • Gastrointestinal – IBD, Bariatric Surgery.
  • UTIs.

Metabolic

  • Nephrocalcinosis.
  • Sarcoidosis.
  • Cystinuria (type A, B, AB).
  • Primary hyperoxaluria (PH).
  • Renal tubular acidosis (RTA).
  • Type I, 2,8-dihydroxyadenine.
  • Xanthinuria.
  • Lesch-Nyhan syndrome.

Structural

  • Cystic fibrosis.
  • Medullary sponge kidney (tubular ectasia).
  • Ureteropelvic junction (PUJ) obstruction.
  • Calyceal diverticulum.
  • Calyceal cyst.
  • Ureteric stricture.
  • Horseshoe kidney.
  • Ureterocoele.
  • Foreign body in the kidney e.g. retained stent.

Medicines

  • Anhydrase inhibitors.
  • Calcium supplements.
  • Vitamin C or D.
  • Probenecid.
  • Triamterene, chemotherapy.