Kidney Stones - Complications

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Excess Oxalate in the Urine (Hyperoxaluria). Oxalate is the most common stone-forming compound. Too much oxalate in the urine is responsible for up to 60% of calcium stones and is a more common cause of stones than excess calcium in the urine.

Hyperoxaluria can be either primary or secondary.

• Primary hyperoxaluria is an inherited disorder in which too much oxalate in the urine is the main problem.
• Secondary hyperoxaluria results from specific conditions that cause high levels of urinary oxalate.

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

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• Severe vitamin B6 deficiencies (usually due to genetic disorders)
• Deficiencies in Oxalobacter formigenes, an intestinal bacteria that breaks down oxalate
• Short bowel syndrome, a condition that generally occurs when portions of the small intestines are removed. It causes an inability to properly absorb fat and nutrients. Calcium may bind to the unabsorbed fat instead of to the oxalates, which causes a buildup of oxalate.
• Androgens (male hormones)

Female hormones (estrogens) actually lower the risk of hyperoxaluria. Estrogen may help prevent the formation of calcium oxalate stones by keeping urine alkaline, and by raising protective citrate levels.

Patients who undergo the most common gastric type of bypass surgery, the Roux-en-Y, may be at increased risk for calcium oxalate kidney stones, beginning 6 months after surgery. The added kidney stone risk is thought to be due to changes in the urine. Patients who have undergone Roux-en-Y gastric bypass surgery have excess oxalate and low levels of citrate in their urine after the procedure.

Another type of weight loss surgery, gastric banding, does not appear to increase the risk for kidney stones.

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 diseases and events: