Kidney Stones

Kidney stones often have no definite, single cause, although several factors may increase your risk.

Kidney stones form when your urine contains more crystal-forming substances (such as calcium, oxalate and uric acid) than the fluid in your urine can dilute. At the same time, your urine may lack substances that keep crystals from sticking together, creating an ideal environment for kidney stones to form.

Knowing the type of kidney stone helps determine the cause and may give clues on how to reduce your risk of getting more kidney stones. Types of kidney stones include:

Most kidney stones are calcium stones, usually in the form of calcium oxalate. Oxalate is a naturally occurring substance found in food. Some fruits and vegetables, as well as nuts and chocolate, have high oxalate levels. Your liver also produces oxalate. Dietary factors, high doses of vitamin D, intestinal bypass surgery and several metabolic disorders can increase the concentration of calcium or oxalate in urine. Calcium stones may also occur in the form of calcium phosphate.

Struvite stones form in response to an infection, such as a urinary tract infection. These stones can grow quickly and become quite large, sometimes with few symptoms or little warning.

Uric acid stones can form in people who don't drink enough fluids or who lose too much fluid, those who eat a high-protein diet, and those who have gout. Certain genetic factors also may increase your risk of uric acid stones.

These stones form in people with a hereditary disorder that causes the kidneys to excrete too much of certain amino acids (cystinuria).

Factors that increase your risk of developing kidney stones include:

• Family or personal history
  If someone in your family has kidney stones, you're more likely to develop stones, too. And if you've already had one or more kidney stones, you're at increased risk of developing another.
• Age
  Kidney stones are most common in adults age 40 and older, though kidney stones may occur at any age.
• Male sex
  Men are more likely to develop kidney stones, although an increasing number of women are developing kidney stones.
• Dehydration
  Not drinking enough water each day can increase your risk of kidney stones. People who live in warm climates and those who sweat a lot may be at higher risk than others.
• Certain diets
  Eating a diet that's high in protein, sodium and sugar may increase your risk of some types of kidney stones. This is especially true with a high-sodium diet. Too much sodium in your diet increases the amount of calcium your kidneys must filter and significantly increases your risk of kidney stones.
• Being overweight
  High body mass index (BMI), large waist size and weight gain have been linked to an increased risk of kidney stones.
• Digestive diseases and surgery
  Gastric bypass surgery, inflammatory bowel disease or chronic diarrhoea can cause changes in the digestive process that affect your absorption of calcium and water, increasing the levels of stone-forming substances in your urine.
• Other medical conditions
  Diseases and conditions that may increase your risk of kidney stones include renal tubular acidosis, cystinuria, hyperparathyroidism, certain medications and some urinary tract infections.

Prevention of kidney stones may include a combination of lifestyle changes and medications:

Lifestyle changes, you may reduce your risk of kidney stones if you:

• Drink water throughout the day
  For people with a history of kidney stones, I would usually recommend passing about 2.5 liters of urine a day. If you live in a hot, dry climate or you exercise frequently, you may need to drink even more water to produce enough urine. If your urine is light and clear, you're likely drinking enough water.
• Eat fewer oxalate-rich foods
  If you tend to form calcium oxalate stones, I may recommend restricting foods rich in oxalates. These include rhubarb, beets, okra, spinach, Swiss chard, sweet potatoes, nuts, tea, chocolate and soy products.
  Choose a diet low in salt and animal protein
  Reduce the amount of salt you eat and choose nonanimal protein sources, such as legumes.
  Continue eating calcium-rich foods, but use caution with calcium supplements. Calcium in food doesn't have an effect on your risk of kidney stones. Continue eating calcium-rich foods unless advised otherwise. Ask your doctor before taking calcium supplements, as these have been linked to increased risk of kidney stones. You may reduce the risk by taking supplements with meals.

Medications can control the amount of minerals and acid in your urine and may be helpful in people who form certain kinds of stones. The type of medication used will depend on the kind of kidney stones you have. Here are some examples:

• Calcium stones. To help prevent calcium stones from forming, I may prescribe a thiazide diuretic or a phosphate-containing preparation.
• Uric acid stones. I may prescribe allopurinol to reduce uric acid levels in your blood and urine and a medicine to keep your urine alkaline. In some cases, allopurinol and an alkalinizing agent may dissolve the uric acid stones.
• Struvite stones. To prevent struvite stones, I may recommend strategies to keep your urine free of bacteria that cause infection.
• Cystine stones. Cystine stones can be difficult to treat. I recommend that you drink more fluids so that you produce a lot more urine. If that alone doesn't help, I may also prescribe a medication that decreases the amount of cystine in your urine.