Types of Stones

The most common type of stone is that of calcium oxalate and phosphate composition. Both calcium and oxalate are chemicals that are found in a normal diet. Stones of this composition make up about 70% to 75% of all kidney stones. Extra calcium is flushed out of the body via the kidneys in normal individuals, but affected patients who develop calcium stones retain the excess. Too much calcium in the urine, a condition known as hypercalciuria, can lead to calcium oxalate stone formation. Almost 2 out of every 5 patients with calcium oxalate stones have an inherited metabolic disorder that causes hypercalciuria. Many drugs like calcium-based antacids and steroids may cause an increase of calcium in the urine. Other factors that could promote elevated calcium levels in the urine include hyperparathyroidism (overactive parathyroid glands), excess dietary vitamin D, and high dietary purine from meat. The parathyroid glands, located in the neck, function in the balance of calcium levels. Removing defective glands from a patient with hyperparathyroidism can solve a patient's problem with kidney stones. Calcium oxalate stones can also be caused by hyperoxaluria, a condition in which there is too much of the salt oxalate in the urine. Excess oxalate production by the body or a lack of dietary calcium can lead to this condition. Large doses of vitamin C or little vitamin B can also lead to hyperoxaluria. Recurrence of calcium containing stones is likely. Pure calcium phosphate stones are less common (6%). They are often associated with conditions such as primary hyperparathyroidism or renal tubular acidosis.

Stones may also be found as a result of bacterial urinary infections, which can cause alkalization of urine. Such stones, which contain magnesium and ammonia, are called struvite stones (or infection stones), and they make up about 15% of all kidney stones. These are more common in women. It is important to remove the stone and prevent recurrence of the urinary infection in these cases. Struvite stones can grow to be very large. They can fill the entire space inside the kidney, in which case they are designated as staghorn calculi. Excess uric acid in the urine (hyperuricosuria), as a result of the body's breakdown of foods like dietary meats, fish, or poultry, can result in kidney stones. They comprise about 8% of all stones. These stones are more common among men and tend to found in acidic urine. Chemotherapy and a metabolic disorder associated with high uric acid levels, also known as gout, are linked to uric acid stones. Cystinuria, another inherited condition, is when too much cystine, an amino acid released by the breakdown of protein from the diet, is collected in the urine. Cystine is insoluble in urine. These stones are rather rare, as they comprise only 1% of all kidney stones.