Diseases & Conditions


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Kidney Stones Overview from the Nephrology Department

What are Kidney Stones?

Kidney stones are small, hard rocks which are made within the kidneys.

What are the symptoms of Kidney Stones?

Sometimes kidney stones cause no symptoms. Other times, they cause blood in the urine and/or severe pain in the side or back. When kidney stones are large or there is more than one, they may block the flow of urine.

Why do Kidney Stones occur?

More than 90% of individuals with kidney stones have a chemical abnormality of blood or urine that contributes to the tendency to form the stones. In all people, not drinking enough water or other fluids may also contribute to forming stones. Inadequate fluid intake causes the kidneys to produce less urine, as well as urine that is highly concentrated. The smaller the daily volume of urine, the more likely it is that a person would form kidney stones. This is especially true if a person has one of the aforementioned chemical abnormalities.

What chemical abnormalities are known to cause kidney stones?

The chemical abnormalities relate to the type of stones that form in the kidneys. These four types of stones and the chemical abnormalities that cause them are:

  • Calcium Stones: people who form this type of stone either have too much of one type of three chemicals in their urine, or not enough of another. In particular, they have either too much calcium, oxalate, or urate in their urine, or too little citrate. Eating too much salt may cause too much calcium to stay in the urine A few patients will have kidney stones from overproduction of the calcium controlling hormone, parathormone. Drinking milk does not cause kidney stones.
  • Struvite Stones: Chronic infection of the urine generally causes these stones. The bacteria responsible for the infection cause a chemical alteration of urine which leads to this type of stone.
  • Uric Acid Stones: This type of stone forms when the urine is too acidic, which causes excessive uric acid production.
  • Cystine Stones: These stones form because of an inherited condition in which the body cannot clear a chemical called cystine from the blood. Usually, other family members have the same condition.

Knowing the type of kidney stone is important to prescribing treatment to prevent other stones from forming.

How are Kidney Stones diagnosed?

If a person is suspected of having kidney stones, either because of pain or blood in the urine, the physician may order x-rays or an ultrasound examination of the kidneys, ureters (tubes that carry urine from the kidneys to the bladder) and the bladder. If present, most kidney stones can be seen on an x-ray, although sometimes an ultrasound examination is necessary to see other types of kidney stones.

How do Kidney Stones leave the body?

In many cases, a person will pass the stone via the urine. This may be a painful process, and may take a couple of days. Generally, the physician asks the person with kidney stones diagnosed by x-ray or ultrasound to strain the urine and save the stone so that it can be analyzed.

When a person cannot pass the stone through the urine, there are treatments available to remove or crush them, including:

  • Inserting a small instrument through the urethra (the tube through which a person passes urine from the body) to “snare” the stone and remove it
  • Shock wave lithotripsy, whereby the stone is crushed. Once the stone is crushed, a person can pass the smaller pieces
  • Surgery

How can you prevent kidney stones?

  • Drink more liquids: Drinking 8-10 glasses of liquid each day helps to keep the urine dilute – which reduces the concentration of stone forming minerals in the urine At least half of the liquid should be water; the other liquids could be any beverages you like.
  • Reduce the amount of salt you eat: Reducing the salt (sodium) in the diet helps to reduce the amount of calcium in the urine which in turn reduces the tendency for calcium stone formation. Dietary salt reduction is best accomplished by not adding salt to your food and by avoiding those high sodium foods such as processed meats, salty convenience foods (regular, boxed or canned soups, noodle or rice mixes) and salty snacks.
  • Be sure your diet contains adequate amounts of calcium: Several years ago it was believed that dietary calcium should be restricted in patients with calcium kidney stones. At least two scientific studies now show that the inclusion of at least two servings of high calcium foods per day in the diet actually reduces the rate at which calcium-containing kidney stones form.
  • Avoid those foods which can increase the amount of oxalate or uric acid in the urine: The following foods should be avoided: chocolate, anchovies, rhubarb, caviar, greens, herring, berries, scallops, peanuts, mussels, asparagus, organ meats (liver, kidneys, brains), tea, meat, extracts, broth, bouillon, consomme.
  • Medications: These should only be prescribed by your physician after the cause for your kidney stones is determined.
    • Hydrochlorothiazide, a diuretic which is very effective in reducing calcium in the urine and preventing kidney stones
    • Sodium bicarbonate taken orally makes the urine less acidic and more alkaline. In turn, this decreases the amount of uric acid and cystine in the urine
    • Penicillamine and/or captopril: These two drugs have been found useful in reducing the excretion of cystine in patients who have this as the cause for their kidney stones
    • Antibiotics: In those patients who have struvite (infection) stones, preventing or controlling urinary infection is mandatory to prevent the recurrence of stones
    • Allopurinol reduces the amount of uric acid excretion