About Kidney Stones

What is a kidney stone?

A kidney stone is simply a mineral deposit that forms in the urinary tract. Kidney stones develop when crystals, which are present in the urine, begin to stick together and gradually build up into a rock-like mass. Initially, kidney stones are quite small in size, but over time, as more and more crystals attach, they can grow quite large.

Why do kidney stones form?

The crystals that form kidney stones are made from substances normally present in the urine. These substances include calcium, oxalate, phosphate, uric acid and other chemicals. Our kidneys normally excrete these chemicals into the urine. However, when their concentration in the urine is very high, these chemicals don't stay dissolved, and instead, begin to “crystallize out” of the urine. There are other substances in the urine, called “inhibitors”, which help to keep the crystals from sticking together. When the concentration of crystals is too high, or the relative amount of inhibitors is too low, a kidney stone will form. Many factors can contribute to your chance of having a kidney stone, including your family history, diet and fluid intake, where you live, or even your work environment.

What are the different types of kidney stones?

There are several different types of kidney stones, each with a different chemical composition. The vast majority of kidney stones contain calcium. Calcium stones are composed of calcium that is chemically bound to either oxalate (calcium oxalate stones) or phosphate (calcium phosphate stones). Of these, calcium oxalate is far more common. Pure calcium phosphate stones are rare, and usually indicate an underlying illness or metabolic disorder. The most common stone composition is actually a mixture of mostly calcium oxalate with a little bit of calcium phosphate. About 15% of kidney stones contain no calcium. These include uric acid stones, struvite stones and cystine stones.

How common are kidney stones?

In the United States, about 1 person in 10 will develop a kidney stone during their lifetime. Last year, kidney stones were responsible for over 600,000 emergency room visits in the United States. We know that men are more likely to have kidney stones than women. Caucasians are 5 times more likely to have kidney stones than African-Americans. The peak incidence is between 40 and 50 years of age, and appears to decline after that.

What are the chances of recurrence?

Kidney stones tend to recur. If a man has had one kidney stone, and does nothing to reduce his risk of recurrence, studies show he has about a 60 to 70% chance of having another. If a man has had two kidney stones, the chances of recurrence go up to over 90%. The odds of recurrence are slightly lower for women.

Getting your kidney stone analyzed

The first step in prevention is to understand which chemical type of kidney stone you are making. So, it is very important to send your stone or stone fragment to the lab for analysis. If you are trying to pass a kidney stone you should strain your urine, catch any stone or gravel that appears, and bring it to your urologist's office. If you have had your stone removed with an extraction procedure, your urologist will send it to the lab for analysis. Finally, patients who undergo shockwave lithotripsy—a procedure which breaks the stone up with sound waves—should carefully strain their urine in the days (and possibly weeks) after the procedure, and bring to their urologist's office any fragments or gravel that appears.

Lab tests

Depending on the chemical composition of your stone, and the number of stones you've had in the past, your doctor may suggest that you undergo specialized lab tests. These tests are designed to measure the amount of certain chemicals in your blood and urine, and detect the specific imbalance or excess which might be causing stones to form. The results of these lab tests may indicate the need for daily use of a prescription medication to reduce the risk of stone recurrence.

DIET AND LIFESTYLE MODIFICATIONS

Dilution is the best solution

The single most effective step to prevent recurrence is to increase your fluid intake. By drinking a total of 8 to 10 glasses of fluid per day, you will dramatically “dilute” your urine, making it less concentrated. This will keep crystals from forming, and reduce the likelihood of stone formation. At least half of the fluid intake should be water. Although 8 ounces of coffee or tea per day has been shown to slightly decrease the risk of stone formation, excessive intake of caffeinated beverages, such as coffee, tea or soda has been shown to increase risk, and should be avoided. If you have trouble determining your fluid status, pay attention to your urine. Dark urine usually means that you are not getting enough fluid. The goal is to drink enough so that your urine is pale in color.

Reduce your protein intake

Studies have shown that increased animal protein intake (i.e.; meat, eggs, cheese, etc.) will lead to higher levels of calcium, uric acid and oxalate in the urine—all of which can increase the risk of calcium stone formation. “Low carb” diets, which are generally high in protein and fat, are NOT recommended for individuals with a history of calcium kidney stones. To reduce your risk of calcium stone formation, reduce your intake of animal protein, and instead, substitute with a few vegetarian meals each week.

Reduce your sodium intake

Studies have consistently shown that higher sodium intakes lead to increased calcium in the urine. Many experts believe that restricting sodium to no more than 2400 mg per day, while increasing fluid intake is one of the most effective means of reducing calcium stone recurrence. Remember, however, that high levels of sodium are found in many prepared foods, and not just in the salt shaker. Whenever possible, reduce your intake of canned or processed foods, look for “reduced-sodium” products, and avoid adding extra salt to your food.

Moderate calcium intake

Contrary to earlier beliefs, dietary calcium—meaning calcium we get from food—is actually not a problem for calcium kidney stone formers. In fact, there is evidence that moderate intake of calcium-containing foods actually protects against stone formation by binding dietary oxalate, and preventing its absorption. So, do NOT eliminate calcium containing foods from your diet unless your doctor advises it. Certain calcium supplements, such as ones containing calcium carbonate, may increase your risk of stone formation. Supplements containing calcium citrate, when taken in appropriate doses, are a safe choice for recurrent stone formers.

Watch your oxalate intake

Your urologist may recommend that you reduce or eliminate your intake of oxalate-rich foods. Foods highest in oxalate include: chocolate or cocoa, spinach, rhubarb, beets, wheat germ, black teas (not green or herbal) nuts (almonds, cashews, hazelnuts, peanuts) and soybeans. If your doctor has recommended that you follow a low oxalate diet, and you would like more information on how to do so, please read the Food Oxalate Content List

Increase your intake of “stone inhibitors”

Several substances found in the urine have been clearly shown to reduce the formation of calcium based kidney stones. Two of the most important are citrate and magnesium. Lemon juice has been found to increase the level of citrate in the urine. Real lemonade (not from a powder mix) is an excellent way to increase both your citrate and fluid intake. Nutritional supplements containing magnesium, potassium and citrate may also help to increase the concentration of “stone inhibitors” in the urine.

Avoid high-dose vitamin C supplements

High-dose vitamin C (ascorbic acid) supplements should be avoided unless otherwise recommended by your healthcare provider. Generally, the amount of vitamin C found in a multivitamin is safe, but higher amounts (>500 mg) from supplements may increase the risk of kidney stone recurrence in those at an increased risk.

Vitamin B6 supplements

Vitamin B6 may be effective in decreasing oxalate production, and therefore vitamin B6 supplements are thought to decrease the risk of calcium oxalate kidney stones. A combination of magnesium oxide and vitamin B6 was shown to increase urinary magnesium and citrate, and decrease urinary oxalate in calcium oxalate stone formers. Ask your urologist before starting any regimen of nutritional supplementation.