Kidney Stones - Complications

Causes

The key process in the development of kidney stones is supersaturation.

• The urine carries salts, including calcium oxalate, uric acid, cystine, or xanthine.
• These salts can become extremely concentrated if there is not enough urine, or if unusually high amounts of crystal-forming salts are present.
• When salt concentration levels reach the point at which they no longer dissolve, these salts form crystals.

Different factors may be involved in either reducing urine amount, or increasing the levels of the salts.

Deficiencies in Protective Factors. Normally, urine contains substances that may protect against stone formation, including:

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• Magnesium
• Citrate
• Pyrophosphate
• Enzymes

These substances:

• Allow salt in the urine to be at higher-than-normal concentrations without forming crystals
• Prevent crystal formation
• Coat the crystals and prevent them from sticking to the surface of kidney tubes

Not having enough of these protective substances can cause stones.

Changes in the Acidity of the Urine. Changes in the acid balance of the urine can affect stone formation.

• Uric acid and cystine stones mainly form in acidic urine.
• Calcium phosphate and struvite stones increase in alkaline urine.

Causes of Calcium Stones

Often, the cause of calcium stones is not known. The condition is then called idiopathic nephrolithiasis. Research suggests that nearly all stones result from problems in the breakdown and absorption of calcium and oxalate. Genetic factors may play a role in about half of these cases. A number of medical conditions and drugs can also affect digestion and intestinal absorption.

Excess Calcium in the Urine (Hypercalciuria). Hypercalciuria (too much calcium in the urine) is responsible for as many as 70% of calcium-containing stones. A number of conditions may produce hypercalciuria. Many are due to genetic factors, but most cases are due to unknown causes (idiopathic).

The following can lead to hypercalciuria and calcium stones:

• Too much calcium absorption in the intestines: In most of these conditions, genetic factors lead to increased calcium absorption in the intestine.
• Excessive chloride: Chloride has a negative charge and calcium has a positive charge, so they balance each other in the body. Excess chloride may lead to excess calcium.
• Renal calcium leak: In this condition, the kidney does not regulate minerals normally, causing an increase of calcium in the urine.
• Excessive sodium: High urinary levels of sodium result in increased levels of calcium. Certain defects in the kidney tubules transport system cause imbalances in sodium and phosphate, which can lead to high calcium levels in the urine. A high-salt diet can also produce this effect.