Kidney Stones - Causes

Causes of Uric Acid Stones

Uric acid stones are formed from crystals made from purine, a nitrogen end product of dietary protein. There are usually three conditions observed in patients with uric stones:

Urine is persistently acidic so that even normal amounts of uric acid can precipitate and form stones. Persistently acid urine is the most important cause of uric acid stones.
Patients produce lower than normal amounts of urine.
Patients have high amount of uric acid in the urine (hyperuricosuria). This is less often a cause of uric acid than acidic or low volume of urine. Hyperuricosuria may be due to a high intake in protein, can be an inherited condition, or is associated with high levels of uric acid in the blood (hyperuricemia). Note: this condition is also common in calcium stones. Therefore, a combination of calcium and uric acid stones may be present in patients with hyperuricosuria.

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A number of conditions may contribute to or cause uric acid stones.

Gout (Uric acid and other kidney stones are present in 10 -25% of patients with primary gout, a prevalence more than 1,000 times that of the general population.)
Possibly kidney abnormalities that reduces ammonia productions, particularly in people with diabetes or insulin resistance
Genetic factors
Hypocitraturia
Diets overly rich in animal proteins
Certain medications (chemotherapy agents, diuretics, and salicylates)
Binge drinking
Fasting
Lead toxicity
Blood diseases (leukemia, certain uncommon anemias, multiple myeloma, and lymphomas)
Chronic diarrhea

Causes of Struvite Stones

Struvite stones are almost always caused by urinary tract infections due to bacteria that secrete certain enzymes. These enzymes, in turn, raise urine concentrations of the ammonia that composes the crystals forming struvite stones. The stone-promoting bacteria are usually Proteus, but may also include Pseudomonas, Klebsiella, Providencia, Serratia, and staphylococci. Women are twice as likely to have struvite stones than men.

Causes of Other Stones

Other stones, including cystine and xanthine stones, are usually due to genetic abnormalities.

Causes of Cystine Stones. Cystine stones develop from genetic defects that cause abnormal transport of amino acids in the kidney and gastrointestinal system leading to a build-up of cystine, one of these amino acids. Researchers have identified two genes responsible for this condition: SLC3A1 and CLC7A9.

Causes of Xanthine Stones. In some cases, xanthine stones may develop in patients being treated with allopurinol for gout.