KIDNEY STONE PREVENTION

The kidneys form the first part of the urinary system. They filter the blood to extract excess fluid and waste products. Urine, once made in the kidneys, travels through a tube on each side called a ureter to the bladder where it is stored until emptied to the outside.

Included within the materials filtered by the kidneys are minerals. Minerals are present in many of the foods that we eat. These minerals are absorbed during the process of digestion. The body uses the minerals which it needs, and the excess are excreted by the kidneys. Calcium, oxalate and uric acid are some of these end products excreted by the kidneys.

Stones can form in the kidneys if an excess amount of calcium, oxalate or uric acid reaches the kidney at one time. If there is too much of one of these substances, it will not stay in solution in the urine. Rather, the minerals can join together and form crystals. Crystals can then join together to form a stone.

The two predominant means to prevent stone formation are adequate hydration and dietary avoidance. Dietary avoidance means avoiding excess amounts of calcium or oxalate in the diet. Adequate hydration means taking in plenty of water or other liquids so that there is enough fluid to reach the kidneys. The kidneys can then make a dilute urine (not a concentrated urine) and stone formation is less likely.

A separate dietary list is available which lists food that are rich in calcium and oxalate. In the Foods Allowed column, no dietary restriction is necessary. In the Foods to Avoid column, moderation is the key. An individual can eat foods in this column but should avoid an excess combination of these foods. If too much calcium and oxalate reach the kidney at the same time, they will begin to crystallize and form stone. An excess of sodium should be avoided too, since this may trigger stone formation.

Even more important than dietary avoidance is adequate hydration. One needs to make sure that there is adequate fluid reaching the kidney to keep the urine dilute. A good rule of thumb is to drink two large glasses of water with each meal. The majority of calcium, oxalate or uric acid reaches the kidney after eating a meal. Two glasses of water with each meal allows plenty of fluid to reach the kidney so that these materials do not become too concentrated and crystallization does not begin.

Finally, a third concept available for preventing stone formation is to increase the level of inhibitors of stone formation. There are some medications which can be used which will raise citrate (not citric acid) level in the urine. A high level of urinary citrate is a natural inhibitor to stone formation. Recent studies have suggested that lemonade made from real lemon juice raises urinary citrate levels and may lessen the risk for stone formation.

For patients with uric acid stones, treatment with Allopurinol may be recommended at times. Allopurinol reduces the level of uric acid formed by the body, which reduces the amount that the kidney has to filter. Allopurinol treatment is effective for lessening the potential for uric acid stone formation, but does not provide any benefit for patients who form calcium oxalate stones. With the above measures, an individual's chance of stone formation can be significantly reduced.