Kidney stones, or urinary calculi, are solid particles that form in your urinary tract. About 80 percent of all urinary calculi in the U.S. contain calcium. Most are made of calcium oxalate. The remainder consist of calcium phosphate, uric acid, cystine or struvite, which is a conglomeration of magnesium ammonium phosphate. About 5 percent of men and women in the U.S. will have a kidney stone during their lifetimes.
Risk Factors
According to Dr. Paul Pietrow, former assistant professor of urology at the University of Kansas Medical Center, several risk factors increase your chances of developing a kidney stone. Some of these factors are associated with underlying medical conditions; others are behavioral. A partial list of risk factors includes a family history of kidney stones, gout, obesity, disorders of the parathyroid glands or kidneys, diabetes, bowel disease, prolonged immobilization and excess consumption of meat, sodium or oxalate.
A Stone Is Born
Renal calculi develop from microscopic crystals that form in the drainage system of your kidneys. Crystal formation is encouraged by low urine volume or increased urine concentration, high levels of urinary ions, excessively acidic or alkaline urine and the absence of natural stone inhibitors, such as citrate. Once established, crystals tend to accumulate layers, much like a hailstone, until they are large enough to cause symptoms.
Symptoms of Kidney Stones
Once a stone has formed, it can interfere with normal urine flow. This may allow bacteria to enter the urinary tract and cause infection. In fact, the stone itself can be colonized by bacteria, making it difficult to completely clear the infection. When a kidney stone begins to move through your urinary tract, it can cause nausea, vomiting, restlessness, urinary frequency and burning, blood in the urine, fever and, most notably, excruciating pain. The pain from a kidney stone tends to migrate with the stone's movement, typically starting high in the back and progressing downward and forward until it emanates from the groin.
Diagnosis
The diagnosis of renal calculi is usually straightforward, although other conditions -- such as a urinary tract infection or a viral illness -- can mimic a kidney stone. Most calcium-containing stones can be seen on a plain X-ray, so this may be one of the first tests performed, in addition to urinalysis and blood work. CT scans, specialized X-rays or ultrasound examinations are also commonly used. Many physicians order a complete evaluation to rule out metabolic problems such as renal tubular acidosis, hyperparathyroidism, gout or bone disease.
Treatment
The initial stone-passing episode can usually be addressed with pain medications, fluids and expectant waiting. Antibiotics are often administered to prevent infection. However, if you have a particularly large stone, specialized treatment at the hands of a urologist may be required. Some larger stones can be retrieved by passing a scope through your bladder and into the upper urinary tract. Others may require open surgery or the use of sound waves to break the stone into smaller pieces that you can pass on your own.
Analysis
It's important to retrieve your kidney stone, if possible, when it passes. Usually, you will be given a special urine strainer so you can return the stone to the laboratory for analysis. Even though most stones contain calcium oxalate, many calculi contain multiple layers of several compounds, and an underlying medical condition may be the root cause of a "run-of-the-mill" stone. Stone analysis helps determine the appropriate approach for preventing more kidney stones.
Prevention
One measure that helps prevent all kidney stones is increased fluid intake. A 1996 study in the Journal of Urology recommends a target of two quarts of urine production daily. Another study cited in the journal demonstrated that a low-salt, low-meat, moderate-calcium diet was more effective for preventing recurrence of calcium-containing stones than a strict, low-calcium diet. If you have a calcium-containing stone, preventive measures vary depending on whether the stone is composed of calcium oxalate or calcium phosphate. Calcium oxalate stones can often be prevented by decreasing the consumption of oxalate-containing foods such as nuts, wheat bran, tea, chocolate, soy, spinach and strawberries. Avoiding excessive vitamin C intake and increasing urinary citrate levels also help prevent calcium oxalate stones. Urinary citrate can be increased by taking Bicitra or Urocit-K, which are sources of sodium citrate and potassium citrate, respectively. Calcium phosphate stones often result from underlying medical conditions, such as hyperparathyroidism, sarcoidosis or kidney disorders. Preventing recurrence may require treatment of the underlying cause in addition to lowering urinary calcium levels and increasing urinary citrate. Treatment for calcium phosphate stones often includes the use of medications, such as Bicitra, Urocit-K and diuretics.
References
- "American Family Physician"; Medical management of common urinary calculi; Pietrow P, Karellas M; 2006
- "The Journal of Urology"; Urinary volume, water, and recurrences in idiopathic calcium nephrolithiasis: a 5-year randomized prospective study; Borghi L, et al.; 1996
- "Indian Journal of Urology"; Dietary modifications for preventing recurrent stones; Yadav R, Kumar R; 2006
