Causes of Renal Lithiasis

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There are various types of urinary stones with different origins:

Calcium molecule with upward pointing arrow indicating a rise

Calcium lithiasis. This is the most common type of lithiasis. It accounts for 70-80% of all lithiasis cases. These stones form due to increased concentrations of calcium in the urine. They are composed of calcium oxalate (36-70%), calcium phosphate (6-20%), or mixtures (different components in the same stone, 11-31%).

This increase in calcium occurs in three situations: 

  • Hypercalciuria. When more than 300 mg of calcium is excreted in the urine each day. This, in turn, is subdivided into three groups:
    • Absorptive. When the excess calcium in the urine is due to increased intestinal absorption.
    • Excretory. When the excess calcium in the urine is due to the kidney eliminating much more calcium than normal.
    • Bone resorptive. When the excess calcium in the urine is due to increased bone resorption of calcium. This leads to elevated calcium levels in the blood, which is compensated for by being excreted in the urine. The most common example of this type of disorder is primary hyperparathyroidism.
  • Hyperoxaluria. This occurs when more than 40 mg of oxalate is excreted in the urine each day. It is subdivided into: 
    • Enteric. This appears after severe episodes of diarrhoea (Crohn's disease, short bowel syndrome, etc.), which causes greater absorption of oxalate from the diet, so that the excess is eventually eliminated by the kidneys.
    • Endogenous (types I and II). This is caused by an alteration in the enzyme that makes oxalic acid, leading to an increase in this acid. 
  • Idiopathic or of unknown cause. These account for 10-25% of calcium lithiasis cases.
  • Struvite or magnesium ammonium phosphate lithiasis, apatite or infectious stones.
Kidneys and urinary system

Infectious lithiasis. These account for 6-20% of all lithiasis. This usually involves large "coral-shaped” stones (with shapes similar to sea coral). They are more frequent in women. They are caused by urine infections resulting from the so-called ureolitic germs. They have this name because they produce urease, an enzyme that causes urea in the urine to be transformed into ammonium and carbonate radicals. When there is a urine infection, the pH of the urine becomes more alkaline and, in this situation, these radicals bind to the magnesium or phosphate in the urine, causing struvite or magnesium calcium phosphate stones; or phosphate in the urine, which leads to carboapatite stones.

Uric acid crystals

Uric acid lithiasis. This accounts for 6-17% of all lithiasis cases. It occurs when more than 600-800 mg of uric acid is excreted in the urine each day (hyperuricosuria). There are three types:

  • Idiopathic (unknown). The vast majority of stones are of this kind. They occur when the urine has an acidic pH (pH < 5.5), which favours the precipitation of acidic substances in the urine in the form of uric acid stones.
  • Hyperuricaemia. This is caused by an increase in uric acid in the blood, as happens, for example, in psoriasis, gout, and so on, and the consequent elimination of this excess acid in the urine.
  • Enterorenal. This is caused by the eating a diet rich in purines. These are absorbed at the intestinal level, leading to an increase in uric acid in the blood and the consequent elimination of the excess in the urine.
DNA

Cystine lithiasis. This is produced when cystine is eliminated in the urine (more than 150-200 mg a day). It is due to a hereditary family disease that causes the kidney to excrete a large amount of several amino acids including cystine. It is the only amino acid that is not soluble in the usual pH of urine and precipitates in the form of stones. It accounts for 0.5-3% of all lithiasis cases. 

Urinary lithiasis

Miscellaneous (other types). These represent 1-4% of all lithiasis cases. One example are xanthine calculi. Xanthinuria is an autosomal dominant hereditary disease (if the abnormal gene is inherited from only one parent, the disease can still develop). It involves a deficit in the xanthine-oxidase enzyme that produces increased xanthine and hypoxanthine in the urine, and these substances are precipitated in the form of stones.

Is hereditary to have kidney stones?

Substantiated information by:

Bárbara Romano Andrioni
Pilar Luque

Published: 16 November 2020
Updated: 16 November 2020

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