Kidney Stone Types

Kidney stones fall under four major categories: calcium, uric acid, struvite, and cystine. The painful stones develop from the buildup of excess chemicals that don't flush out through the kidneys. Some types are more common than others, but all are unique based on their individual chemical structure.

Calcium

• The most common type of kidney stone is composed of oxalate or phosphate calcium. These stones can form in the kidneys as a result of high levels of calcium and vitamin D, low levels of urinary citrate and magnesium, or an inadequate urinary volume. They can also form from high oxalate, sodium and uric acid levels present in the blood and urine.

Uric Acid

• The second most common type of kidney stone is composed of uric acid. Excess uric acid present in the urine attaches to the walls of the kidneys, clumps together and forms stones. They are commonly caused by digesting and metabolizing meat proteins. Uric acid kidney stones are more commonly seen in people suffering from gout, or those who are receiving chemotherapy treatment. Unlike other kidney stones, they can be dissolved with medication.

Struvite

• Struvite stones, also called infection stones or triple phosphate stones, are composed of calcium, ammonia and phosphate. They develop from a chemical imbalance in the urine and an overproduction of ammonia. As bacteria in the urinary tract counterbalances the urinary acid, it allows the bacteria to multiply out of control. Struvite kidney stones are more commonly seen in urinary tract or bladder infections and are typically seen more in women than in men. Recurring urinary tract infections can be a contributing risk factor for developing struvite stones.

Cystine

• Cystine kidney stones are rare and are usually related to Cystinuria, a hereditary genetic disorder that strikes mainly children and young adults. Cystine stones are formed due to an abnormal gene that negatively affects the absorption of amino acids by the kidneys. The condition usually presents itself at birth, and children with a family history of cystine stones are more likely to develop them.

Other

• Kidney stones can be formed as a combination of types. The incidence of one type of kidney stone may put a person at risk for another. An inherited medical condition called xanthinuria can cause xanthine stones. Kidney stones can be caused by other drugs, such as triamterene and the protease inhibitor indinavir for the treatment of HIV. Rarely, kidney stones can also develop from taking herbal supplements such asephedrine, gualfenesin, or supplements containing silica.