Common Types of Kidney Stones

Calcium Oxalate and Phosphate Stones
Calcium oxalate and phosphate stones are made up of a hard crystal compound and are the most popular of the stones with about 70% to 80% of all kidney stones currently made up of calcium oxalate and phosphate. Calcium oxalate is often mixed with phosphate, but either pure calcium oxalate or calcium phosphate stones may occur.

The cause of calcium oxalate appears to be too much calcium in the urine or too much oxalate in the urine. This can result from too much oxalate production by the body or not enough calcium in your diet. Large doses of vitamin C or not enough vitamin B can also lead to excess oxalate in the urine.

Struvite (or infection) Stones
About 10% to 28% of all stones are associated with bacterial urinary infections and most common in women. In patients with struvite stones, it is important not only to remove the stone but also to prevent recurrence of the urinary infection.

Uric acid stones.
About 5% to 13% fo kidney stones contain uric acid, which arises when the body breaks down certain foods, especially meats. These stones are more common among men and develop when there is too much uric acid in the urine. Patients with gout, a metabolic disorder associated with high uric acid levels, are especially prone to uric acid stones as well as a diet high in purine from meat, fish, and poultry.

Cystine stones
Another inherited condition can cause too much cystine (produced by the breakdown of protein from your diet) to collect in the urine. The cystine tends to form crystals that develop into cystine stones. These stones are relatively rare, accounting for only about 1% to 3% of all kidney stones.

Kidney stones can become stuck in any part of the urinary system. To begin to locate a stone, doctors may perform an x-ray or ultrasound study. This gives a good idea of the stone’s size and where it is located. Many patients also receive an intravenous pyelogram (IVP). For an IVP, a special dye is injected into the patient’s vein. The dye eventually collects in the urinary system. There, it produces a white contrast when an x-ray is taken. The dye allows the doctor to precisely locate the stone and to determine the condition of the kidneys, ureters, and bladder.

It is very important that the stone, if passed, be saved, so that it can be sent to a laboratory for evaluation. Long-term treatment and prevention plans depend on the type of stone. Between 70% and 80% of stones pass on their own in the urine, usually within 48 hours of the start of the symptoms. To catch a stone, patients are asked to urinate into a strainer, a cup with mesh in the bottom. All pieces of stone, no matter how small, should be collected and given to the doctor. If one stone is analyzed, more may not be needed, since most people develop just one type of stone.

Although kidney stones, especially calcium stones, are very hard, most of the 20% to 30% that do not pass out of the body on their own can be eliminated without surgery. A process called lithotripsy (from the Greek word for “stone crushing“) breaks into tiny fragments most stones that are less than three-quarters of an inch acress. (Lithotripsy also is called extra-corporeal shock wave lithotripsy.)

Lithotripsy has been used in the U.S. since 1984. It is performed using a machine called a lithotripter. There are different types of lithotripters, but all focus shock waves from outside the body on the kidney stone. Repeated shock waves cause the kidney stone to disintegrate into tiny particles. These particles pass easily out of the body in the urine.

Before receiving lithotripsy, the patient’s history is reviewed and the physical examination is completed. Laboratory tests also are performed, and the patient may be given some medication. Just before lithotripsy, most patients receive a sedative to help them relax. Occasionally, a patient is given anesthesia - either general anesthesia, which induces a sleep-like state, or a regional anesthesia, which numbs the lower body. The choice depends on physician and patient preference. Shock waves are then focused on the kidney stone for a total time of one-half hour to two hours. As the shock waves travel through body tissue, they may cause some mild bruising, which heals in a few days.

In addition to lithotripsy, some patients may need to have a tube (catheter) inserted via a needle through the back muscles into the kidney to help drain the kidney. This tube may later be used to remove stones through a small telescopic device. Also, stones located in the lower portions of the urinary system may be removed with a small telescope inserted through the urethra. In fewer than 5% of cases, surgery through an incision may be required to remove kidney stones.
People who have had one kidney stone are prone to develop others. Without preventive treatment or changes in lifestyle, patients can develop a new stone within a year or two of the first one. About half of patients do develop a stone again within 5 to 10 years, and 80% do so sometime in their lives