How Are Oxalate Kidney Stones Formed?

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Kidney Stone Formation

The urine normally contains substances that inhibit mineral crystals from forming and remaining in the urinary tract. These substances do not work effectively in some people, leading to consistent formation of mineral crystals. When the crystals remain tiny, they pass out of the body in the urine without notice. When the crystals grow too large to pass out of the body naturally, they cause severe pain and may require medical intervention to prevent damage to the structures of the urinary tract.


Kidney stones form from several types of minerals. The most common type of kidney stone forms from calcium combined with oxalate or phosphate. Since these substances are a natural part of the diet, there’s no way to completely avoid them. Calcium oxalate kidney stones form in several shapes. Smooth stones do not have any rough edges. Staghorn and jagged stones have sharp edges that can damage the lining of the urinary tract and cause bleeding.

The body also produces oxalate in addition to the oxalate found in a number of foods. In a condition known as hyperoxaluria, the body produces too much of this substance and the substances in the urine cannot dissolve all of it. This leads to the formation of oxalate crystals that cause kidney stones.


Those who have a high risk for developing oxalate kidney stones may have to avoid high-oxalate foods and eat low- to medium-oxalate foods in moderation. High-oxalate foods include chocolate, sweet potatoes, okra, peanuts, beets, Swiss chard, spinach, beets, rhubarb, wheat germ, black Indian tea and soybean crackers, according to the National Kidney and Urologic Diseases Information Clearinghouse. Medium-oxalate foods include liver, strawberries, marmalade, red raspberries, grapes, grits, green pepper, celery, and fruit cake.


If a low-oxalate diet does not prevent the formation of stones in the urinary tract, surgical intervention may be necessary. Doctors perform surgery when the stone is too large to pass, causes a chronic urinary tract infection, blocks the flow of urine, causes constant bleeding, or grows larger. Several types of surgical treatments are available for treating kidney stones.

Extracorporeal shock wave lithotripsy (ESWL) uses shock waves that pass through the skin and hit dense kidney stones. These shock waves break the kidney stones up so they can pass out of the body normally. The benefits of this procedure include a short recovery time and the ability to have ESWL done on an outpatient basis. Complications of ESWL include abdominal pain, back pain and blood in the urine.

Doctors use percutaneous neprholithotomy for large kidney stones and stones located in areas that make ESWL impossible. During percutaneous nephrolithotomy, a surgeon makes an incision in the back and uses a nephroscope to locate and remove the kidney stone. Large stones may require the use of an energy probe to break them up into small pieces. After this procedure, the doctor may leave a nephrostomy tube in place so the patient can heal.