Kidney Stones - Complications

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The following can lead to hypercalciuria and calcium stones.

• Too much calcium absorption in the intestines. In most of these conditions, genetic factors conspire to increase calcium absorption in the intestine. Researchers are investigating a possible defective gene that regulates calcitriol, a form of vitamin D, which, in excess levels, may increase intestinal absorption of calcium.
• Excessive chloride. Chloride has a negative charge and calcium a positive one, so they are often used by the body to balance each other. Excess chloride may lead to excess calcium. A gene known as CLCN5, which regulates chloride in the urine, is defective in many patients with calcium stones.
• Renal calcium leak. This is a condition in which the filtering processes in the kidney fail, causing an increase of calcium in the urine.
• Excessive sodium. High urinary levels of sodium result in increased levels of calcium. Defects in the kidney tubules transport system that cause imbalances in sodium and phosphate can lead to high calcium in the urine. A high salt diet can also produce this effect.

Excess Oxalate in the Urine (Hyperoxaluria). Oxalate is the most common stone-forming compound. Excessive oxalate in the urine (hyperoxaluria) is responsible for about 30% of calcium stones and is a more common cause of stones than too much calcium in the urine.

Hyperoxaluria is defined as either primary or secondary.

• Primary hyperoxaluria is an inherited disorder in which excess oxalate in the urine is the main problem.
• Secondary hyperoxaluria is caused by specific conditions that result in excess urinary oxalate.

Secondary hyperoxaluria is usually caused by too much dietary oxalates (found in a number of common vegetables, fruits, and grains) or by abnormalities in the body's break down of oxalates. Such defects may be due to various factors:

• Severe vitamin B6 deficiencies (usually due to genetic disorders)
• Deficiencies in Oxalobacter formigene,an intestinal bacteria that degrades oxalate
• Short bowel syndrome, a condition that makes the intestines unable to properly absorb fat and nutrients; calcium may bind to unabsorbed fat instead of oxalates, which causes excess oxalate
• Androgens (male hormones)