Kidney Stones - Causes

Excessive Calcium in the Bloodstream (Hypercalcemia). Hypercalcemia generally occurs when bones break down and release too much calcium into the bloodstream. This is a process called resorption. It can occur from a number of different things.

Hyperparathyroidism. Overactive parathyroid glands cause about 5% of calcium stones. People with this disorder have at least a 20% chance of developing kidney stones. Women are more likely to have this disorder than men.
Immobilization. Lack of movement can lead to kidney stones.
Renal tubular acidosis, a disorder that causes acid and alkaline imbalance. It not only increases calcium levels in the bloodstream, it also reduces citrate levels.

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High Levels of Uric Acid (Hyperuricosuria). High levels of uric acid in urine are referred to as hyperuricosuria and occur in between 15 - 20% of people (mostly men) with calcium oxalate stones. (Hyperuricosuria is not related to the acidity of the urine itself.) In such cases, urate (the salt formed from uric acid) creates a crystal nidus (the nucleus of a crystal), around which calcium oxalate crystals form and grow. Such stones tend to be severe and recurrent and appear to be strongly related to a high intake of protein. (Hyperuricosuria also plays a major role in some uric acid stones.)

Low Urine Levels of Citrate (Hypocitraturia). Citrate is the primary agent for removal of excess calcium. It also inhibits the process that turns calcium crystals into stone. Low levels in the urine, known as hypocitraturia, are a significant risk factor for calcium stones. In addition, hypocitraturia also increases the risk for uric acid stones. This condition most likely contributes to about a third of all kidney stones.

Many conditions can reduce citrate levels, but often the causes of hypocitraturia severe enough to cause stones are unknown. Some causes include:

Renal tubular acidosis
Potassium or magnesium deficiency
Urinary tract infection
Kidney failure
Chronic diarrhea

Low Levels of Other Stone-Inhibiting Compounds. In addition to citrate, other substances in urine also prevent calcium from precipitating out or forming calcium stones. Some of these include nephrocalcin-A and uropontin (molecules known as glycoproteins), glycosaminoglycan, magnesium, and pyrophosphate.

Nanobacteria Infection. An interesting focus of investigation is the discovery of extremely tiny infectious agents, termed nanobacteria. (Although their name implies bacteria, it is not even clear if these are living things.) Nanobacteria are able to pass from the blood into urine and coat themselves with mineral deposits that resemble the composition of kidney stones. Cells infected with these agents develop mineral deposits both on the inside and outside. Researchers hypothesize that nanobacteria may form the cores of the kidney stones in many people.