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Kidney Stones

Illustration of the anatomy of the urinary system, front view
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What is a kidney stone?

Kidney stones are hard objects, made up of millions of tiny crystals. Most kidney stones form on the interior surface of the kidney, where urine leaves the kidney tissue and enters the urinary collecting system. Kidney stones can be small, like a tiny pebble or grain of sand, but are often much larger.

The job of the kidneys is to maintain the body's balance of water, minerals and salts. Urine is the product of this filtering process. Under certain conditions, substances normally dissolved in urine, such as calcium, oxalate and phosphate, become too concentrated and can separate out as crystals. A kidney stone develops when these crystals attach to one another, accumulating into a small mass, or stone.

Kidney stones come in a variety of mineral types:

  1. Calcium stones: Most kidney stones are composed of calcium and oxalate. Many people who form calcium containing stones have too much calcium in their urine, a condition known as hypercalciuria There are several reasons why hypercalciuria may occur. Some people absorb too much calcium from their intestines. Others absorb too much calcium from their bones. Still others have kidneys that do not correctly regulate the amount of calcium they release into their urine. There are some people who form calcium oxalate stones as a result of too much oxalate in the urine, a condition known as hypercalciuria In some cases, too much oxalate in the urine is a result of inflammatory bowel disease, such as Crohn's disease or ulcerative colitis, or other times it may be a consequence of prior intestinal surgery. Calcium phosphate stones, another kind of calcium stone, are much less common than calcium oxalate stones. For some people, calcium phosphate stones form as a result of a medical condition known as renal tubular acidosis.

  2. Struvite stones: Some patients form stones that are composed of a mixture of magnesium, ammonium, phosphate and calcium carbonate, which is known as struvite. These stones form as a result of infection with certain types of bacteria that can produce ammonia. Ammonia acts to raise the pH of urine, which makes it alkaline and promotes the formation of struvite.

  3. Uric acid stones: Uric acid is produced when the body metabolizes protein. When the pH of urine drops below 5.5, urine becomes saturated with uric acid crystals, a condition known as hypercalciuria. When there is too much uric acid in the urine, stones can form. Uric acid stones are more common in people who consume large amounts of protein, such as that found in red meat or poultry. People with gout can also form uric acid stones.

  4. Cystine stones: Cystine stones are rare, and they form only in persons with an inherited metabolic disorder that causes high levels of cystine in the urine, a condition known as cystinuria.

How are kidney stones diagnosed?

Most people are diagnosed with kidney stones after the thunderclap onset of excruciating and unforgettable pain. This severe pain occurs when the kidney stone breaks loose from the place that it formed, the renal papilla, and falls into the urinary collecting system. When this happens, the stone can block the drainage of urine from the kidney, a condition known as renal colic. The pain may begin in the lower back and may move to the side or the groin. Other symptoms may include blood in the urine (hematuria), frequent or persistent urinary tract infections, urinary urgency or frequency and nausea or vomiting.

When your doctor evaluates you for a kidney stone, the first step will be a complete history and physical examination. Important information regarding current symptoms, previous stone events, medical illnesses and conditions, medications, dietary history and family history will all be collected. A physical examination will be performed to evaluate for signs of a kidney stone, such as pain in the flank, lower abdomen or groin.

Your doctor will perform a urinalysis, to look for blood or infection in the urine. A blood sample will also be collected so that kidney function and blood counts can be measured.

Even though all of these tests are necessary, a kidney stone can only be definitively diagnosed by a radiologic evaluation. In some cases, a simple X-ray, called a KUB , will be adequate to detect a stone. If your doctor requires more information, an intravenous pyelogram (IVP) or a computed tomography (CT) scan may be necessary.

Sometimes kidney stones do not cause any symptoms at all. Such painless stones can be discovered when your doctor is looking for other things on X-rays. Sometimes, although a stone does not cause any pain, it can cause other problems, such as recurring urinary tract infections or blood in the urine.

How can kidney stones be prevented?

If you have had one kidney stone, you are likely to form another. To reduce your chances of forming another stone, the first step is to determine why your original stone formed in the first place. At the Brady Urological Institute, we believe in the adage, “An ounce of prevention is worth a pound of cure,” so we place great emphasis on a thorough metabolic evaluation, so that therapies can be appropriately directed towards reducing the risk of recurrent stone disease.

If you passed your stone on your own and still have it, your doctor will send it to a laboratory to be analyzed to see what it is made of. Usually, if your stone is removed by ureteroscopy or PERC , your doctor will send a piece of the stone for analysis too. The composition of a stone is an important piece of information to have, as treatment is specific to the type of stone.

Because we know that kidney stones form when the urine has too high a concentration of crystals and/or not enough substances that protect against the crystals, a detailed analysis of the metabolism of a stone former is important. Typically, the metabolic evaluation of a stone former consists of a simple blood test and two 24-hour urine collections.

The results of these metabolic studies will provide an assessment of the risk of future stone formation. One or more of the following diagnoses and treatments may be made based on these metabolic data.

Diagnosis: Low urine volume


Increase fluid intake

The most basic thing you can do to prevent stone formation is to drink more fluids, thereby diluting your urine. Your goal should be to urinate more than two liters per day.

All fluids count toward this goal, but water is, of course, the best.

Diagnosis: Too much calcium in the urine (hypercalciuria)

Possible treatments:

Thiazide diuretics

These drugs help to decrease urine calcium excretion. They also help to keep calcium in the bones, reducing the risk for osteoporosis. The most common side effect of thiazide diuretics is potassium loss, so in many cases your doctor will prescribe a potassium supplement to go along with the thiazide diuretic.

Lower sodium intake

The human body carefully regulates its sodium levels. When excess sodium is excreted in the urine, calcium is also excreted proportionally. In other words, the more sodium you consume, the more calcium that will be in your urine. Your goal should be to reduce your sodium intake so that you consume less than 2 grams of sodium per day. Watch out for “silent sources” of salt, such as fast foods, packaged or canned foods, softened water and sports drinks.

Normal calcium diet

People who form stones sometimes think that because there is too much calcium in their urine, they should restrict their calcium intake. There is no research that supports this practice. Your body needs dietary calcium to support the skeleton. You should be encouraged to consume two servings of dairy (between 800 mg and 1,200 mg per day) or other calcium-rich foods to maintain bone stores of calcium.

For patients who form calcium oxalate stones, it is doubly important to consume adequate dietary calcium, because under normal circumstances calcium and oxalate bind together in the intestine and are eliminated from the body. If there is no calcium to join with oxalate, the oxalate will be reabsorbed by your body and passed into the urine where it may increase the risk of calcium oxalate stones.

Increase fluid intake

No matter what your diagnosis, you should drink enough water to produce at least 2 liters of urine per day.

Diagnosis: Hypocitraturia (too little citrate in the urine)

Possible treatments:

Citrate supplementation

Citrate is a molecule that binds to calcium in the urine, preventing calcium from binding to oxalate or phosphate and forming a stone. If your potassium level is low or normal, your doctor may prescribe potassium citrate supplement. If you have high blood potassium levels, your doctor may prescribe a sodium citrate supplement, such as Bicitra or sodium bicarbonate.

There is some evidence that citrus juices, such as orange juice or lemonade, may increase urinary citrate levels, so these fluids would be particularly good for patients with hypocitraturia.

Diagnosis: Hyperoxaluria (too much oxalate in the urine)

Possible treatments:

Low oxalate diet

If you form calcium oxalate stones, it is important that you limit your intake of dietary oxalates. Many healthy foods contain oxalate, so rather than exclude these foods entirely, we ask that you limit those foods that are particularly high in oxalate. If you do consume foods high in oxalate, be sure to flush out the extra load of oxalate with an added glass or two of water.

Normal calcium diet

Oxalate and calcium bind together in the intestine and leave the body together in the stool. If there is not enough calcium, then the extra oxalate will have nothing in the intestine to bind to, so it will be absorbed into the bloodstream and end up in the urine, where it will form a calcium oxalate stone.

Increase fluid intake

No matter what your diagnosis, you should drink enough water to produce at least 2 liters of urine per day.

Diagnosis: Hyperuricosuria (too much uric acid in the urine)

Possible treatments:

Low-protein diet

Most Americans far exceed the necessary protein intake, which can lead to too much uric acid in the urine. As a general recommendation, limit your daily protein intake to 12 ounces per day of beef, poultry, fish and pork. Twelve ounces is equivalent in size to about three decks of cards. This will be plenty of protein to meet your body’s needs.


If you have tried a low-protein diet and you still have too much uric acid in your urine, your doctor may prescribe the drug allopurinol. This drug acts to reduce the uric acid levels in the urine by blocking the conversion of purines to uric acid.

Increase fluid intake

No matter what your diagnosis, you should drink enough water to produce at least 2 liters of urine per day.

Diagnosis: Low urine pH (too much acid in the urine)

Possible treatments:

Citrate supplementation

Citrate supplements, such as potassium citrate, will raise the pH of your urine, making stones, such as those composed of uric acid, less likely to form. If your blood potassium level is high, your doctor may prescribe sodium bicarbonate or Bicitra.

Lower protein intake

A diet high in protein will reduce urinary pH. As a general recommendation, limit your daily protein intake to 12 ounces per day of beef, poultry, fish and pork. Twelve ounces is equivalent in size to about three decks of cards. This will be plenty of protein to meet your body’s needs.

Increase fluid intake

No matter what your diagnosis, you should drink enough water to produce at least 2 liters of urine per day.

When should a kidney stone be treated?

When a kidney stone causes pain to the extent that the pain cannot be controlled with oral pain medication, the stone should be treated. Similarly, stones that are associated with severe nausea or vomiting should be treated. Some stones are associated with infection or fever — such situations can be life threatening and demand prompt attention. Stones that are associated with a solitary kidney, poor overall kidney function or complete blockage of urine flow should also all be treated.

Sometimes, when a stone is associated with bothersome symptoms, it may be appropriate to wait and see if the stone will pass on its own. If the stone is small, this is a very reasonable course of action. However, stones larger in size than 5 mm are unlikely to pass on their own and should be considered for treatment.

If the kidney stone is not causing any symptoms, should I still be treated?

There are some instances when it is OK to leave a kidney stone untreated. If the stone is small (less than 5 mm) and not causing any pain, there is a good chance that it will pass on its own after it falls into the ureter. Such stones may be followed with "watchful waiting." This means that the stone is not actively treated, but instead your doctor keeps a check on the stone to be sure that it is not growing or changing. This can be done with periodic X-rays.

There are a number of reasons to treat a kidney stone even if it is not causing any painful symptoms.

Recurring urinary tract infections

Some kidney stones may be infected, and in many cases, despite proper antibiotic treatment, the infection cannot be cleared from the stone. In such cases, the only way to remove the infection completely is to remove the stone.

Staghorn stones

These are extremely large stones that grow to fill the inside of the kidney. There are serious health risks associated with these stones, and left untreated they are associated with an increased risk of kidney failure.

Occupational requirements

For example, the Federal Aviation Administration will not allow a pilot to fly until all stones have been cleared from his or her kidney. Other occupations also do not allow for the unplanned passage of a kidney stone.

Extensive travel

The patient who, whether for business or otherwise, travels to locales where medical care is not reliable may wish to consider preventive treatment.

Patient preference

After thorough consideration of all options available to them, many patients elect to remove their stones at a time when it is convenient for them.

How should my kidney stone be treated?

Historically, the treatment of kidney stones required major surgery and was associated with long hospitalization and recovery periods. However, in recent years an improved understanding of kidney stone disease, along with advances in surgical technology, has led to the development of minimally invasive and even noninvasive treatments for people with kidney stones.

At Johns Hopkins, we believe that the treatment of a patient’s stones requires an approach that is unique to that individual. We offer a complete range of state-of-the-art treatment options, including ESWL , ureteroscopy and PERC, and we will discuss with you the advantages and disadvantages of each therapy as they apply to your situation. Our goal is to provide each patient with a clear understanding of the nature of their stone burden as well as the most appropriate course of treatment.

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