In general, the most frequent cause of calcium kidney stones is hypercalciuria (an excessive amount of calcium in the urine). About 1/3 of the time there is a family history of calcium stones, although many adults who have passed one or more stones are undiagnosed unless the stone has been retrieved, analyzed and found to contain calcium and/or a 24 hour urine collection has been done to measure the amount of calcium.
To reduce the risk that a new calcium stone will form, we recommend:
- Lowering the concentration of calcium in the urine by making the urine as dilute as possible. This is accomplished by drinking as least 3 quarts of fluid (water is preferable) per day for the teenager; the recommended amount is scaled down proportionally for younger children. This is the most important of all therapies, but the most difficult to accomplish.
- Lowering the amount of salt (sodium) in the diet will lower the amount of calcium in the urine to a moderate degree. Restricting dietary calcium is not effective and is unwise in growing children.
- Medication to lower amount of calcium in urine.
Hydrochlorothiazide, a medicine used primarily as a diuretic to relieve swelling from retained water and for high blood pressure. It has the “side effect” of lowering urine calcium. When combined with low salt diet, it is very effective in lowering urine calcium, but since it increases the amount of potassium excreted in the urine, the diet should have sufficient high potassium foods, such as fruits and vegetables. Also, in the presence of vomiting +/or diarrheal illness, it may increase the risk of dehydration, so it should be stopped until the illness resolves.
Some patients form calcium stones because they don’t have enough citrate in their urine. Sufficient urine citrate inhibits urine calcium from forming stones with oxalate or phosphate. Potassium citrate combines the potassium in everyone’s diet with citrate, also found in citrus fruits, which complexes with calcium in the urine to form a chemical compound which is more soluble than calcium oxalate or calcium phosphate. Unfortunately, the pills are large and the liquid (you have to drink a lot of it) has an unpleasant taste.
- Some patients benefit from both hydrochlorothiazide and potassium citrate therapy in combination.