Regardless of the type of stone a patient has, dehydration is usually a major contributing factor to stone formation. The predisposition to stone formation may be hereditary as up to 25% of patients with stones have a family history of urinary calculi. Diet can also influence stone formation. Excessive intake of calcium (medications) or oxalate (ice tea, colas, green leafy vegetables) can cause stones to form. Some patients have kidneys which leak too much calcium into the urine. Others have recurrent urinary tract infections with a type of organism which raises urinary pH causing a stone to form. Certain diseases can predispose patients to stone formation - hyperparathyroidism (causes calcium loss from bones), renal tubular acidosis (causes a deficiency in urinary citrate, a stone inhibitor), gout, inflammatory bowel disease, and medullary sponge kidneys.

Types of Renal Stones

There are various types of urinary stones, but the most common ones are calcium oxalate, uric acid, struvite and cystine stones.

1. Calcium Oxalate - The most common type of stone. Can be due to excess amounts of calcium or oxalate in the urine. These stones come in 2 different types - monohydrate and dihydrate. Calcium oxalate dihydrate stones usually break easily with lithotripsy (see treatment below for explanation). Monohydrate stones are among the most difficult stones to fragment.

2. Calcium Phosphate - These stones often occur in people with hyperparathyroidism, medullary sponge kidneys, or renal tubular acidosis.

3. uric acid - Unlike the stones listed above, these stones contain no calcium in their pure form. For this reason, they are not visible on X-rays. Patients with gout often develop these stones, but most patients who have these stones do not have gout. Uric acid stones form in acidic urine and often dissolve when the urine is alkalinized.

4. Cysteine - Unlike the other types of stones, these stones have a protein matrix due to excess amounts of the amino acid cysteine in the urine (cystinuria). Cystinuria is an inherited condition and is uncommon. These stones are very difficult to fragment with lithotripsy because of the protein matrix.

5. Struvite - These stones occur in patients with urinary tract infections. Organisms which alkalinize the urine can cause struvite stones to form.