All About Kidney Stones
A kidney stone is a solid piece of material that forms in the kidney out of substances normally dissolved in the urine. Each year, about 1 million people in the United States are diagnosed with the disorder.
Kidney stones are more common in Caucasians than in African Americans. They typically strike between ages 20 and 40. Once a person gets one stone, he or she is more likely to develop others.
How stones form
The urinary tract consists of kidneys, two bean-shaped organs about the size of your fist; two narrow muscular tubes, the ureters, which drain urine from each kidney into the bladder; the bladder, which temporarily stores urine; and the urethra, the tube that empties urine from the bladder. The kidneys make urine by removing extra water and waste from the blood stream. They also maintain the balance of certain chemicals in the bloodstream.
Kidney stones form from chemicals in urine, such as calcium, oxalate, and phosphate. They begin as crystals that build up inside the kidney. Crystals that remain small can pass from the body undetected through the urine. But, if they grow larger and become stones, they can become lodged in the ureter and block the flow of urine, causing infection and pain.
About 75 percent of kidney stones contain calcium, in combination with either oxalate or phosphate. A less common type of stone is caused by urinary tract infections. It is known as a struvite, or an infection stone, and is made of magnesium ammonium phosphate. Struvite stones make up about 10 to 15 percent of kidney stones. About 10 percent of the remaining stones are made of uric acid, which is formed from purine, a nitrogen compound found in protein, and made in the liver. Less than 3 percent of stones are made of the amino acid cystine.
Stones can range from a grain of sand to golf ball size.
Salts in the urine
The underlying causes of kidney stones are not entirely known, but a key factor in the process is super-saturation of the salts carried in the urine (calcium oxalate, uric acid, and cystine). The concentration of these salts can increase when urine volume is decreased or the levels of the salts are increased. When the concentration reaches a point at which the salts no longer dissolve, they form crystals. Normally, the urine contains chemicals such as magnesium, citrate, pyrophosphate, and various proteins and enzymes that prevent the formation of crystals, or prevent crystals from sticking to the inner surface of the kidney.
"When we evaluate a patient with stones, we analyze 24-hour urine samples for stone-forming risk factors," notes Glenn M. Preminger, M.D., a urology surgeon and kidney stone specialist in Durham, N.C.
The most common causes of kidney stones are gastrointestinal disease, kidney disease, urinary tract infections, and a metabolic disorder such as hyperparathyroidism. In other words, changes in the way a person's body metabolizes food and drink lead to an increased likelihood of developing crystals and, in turn, stone disease.
Kidney stones also tend to run in families.
Rare disorders that can cause kidney stones include renal tubular acidosis, sometimes a hereditary disease; cystinuria (crystals of cystine form) and hyperoxaluria (crystals of oxalate form). Absorptive hypercalciuria is a condition in which the body absorbs too much calcium from food and excretes the extra calcium into the urine. This extra calcium forms crystals, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
Kidney stones are more common in people with hypertension, hyperuricosuria (a disorder of uric acid metabolism), or gout, or who consume too much vitamin D and have a blockage or infection of the urinary tract.. Some diuretics or calcium-based antacids may increase the risk of kidney stones because they boost the amount of calcium in the urine. People who have inflammatory bowel disease (Crohn's disease and ulcerative colitis) or who have had an intestinal bypass or ostomy surgery may be at risk for stones.
Making a diagnosis
Unfortunately, there are no true "warning signs" for kidney stones. Small stones are usually passed unnoticed. Large stones often remain undetected until they become lodged in the ureter and the person has severe and sudden pain in the back or lower abdomen. The pain is usually described as a sharp and cramping pain in the back, the side, or in the lower abdomen. The pain may spread to the groin. There may also be blood in the urine, nausea, and/or vomiting. If the stone is too large to pass, the muscles of the ureter tighten trying to squeeze the stone into the bladder. Fever or chills mean there is an infection.
Most kidney stones can be diagnosed by an X-ray. A sonogram can also spot a stone. These images tell the doctor the stone's size and location. Blood and urine tests help detect any abnormal substance that might promote stone formation.
The doctor may decide to scan the urinary system using a CT scan or a special X-ray test called an intravenous pyelogram (IVP). The results of these tests and the others above help determine the appropriate treatment.
Getting the stone out
For the vast majority of stone sufferers, treatment means allowing the stone to pass naturally. Your doctor may give you medication for pain relief, and then add fluids until the ureter builds up enough pressure to push the stone out. If the stone hasn't passed in eight to 12 hours, a urologist may be called in to push the stone back to the kidney so it can be broken up.
For stones that don't pass on their own, alternative treatments are used. Extracorporeal shock wave lithotripsy (ESWL) directs shock waves through the skin and body tissue toward the stone. The shock waves break the stone into small fragments that can pass from the body in the urine.
For stones too large or unable to be reached with ESWL, doctors may use percutaneous stone removal. With this procedure, a surgeon makes a small incision in the person's back and creates a tunnel to the kidney. The stone is then removed through a nephroscope. If the stone is very large, the surgeon can insert an energy probe to break it into smaller pieces and remove the fragments.
Ureteroscopic stone removal is another procedure, but it requires no incision. Instead, the surgeon inserts a fiber optic instrument into the urethra and the bladder and then runs it into the ureter. After the stone is located, it's removed with a cage-like basket device or shattered with laser beams or shock waves. Often, a stent is placed in the ureter to keep the tube dilated and ease passing of the fragments.
"Twenty years ago, the only option for removal of stones was open surgery," Dr. Preminger says. "Now, open surgery is performed less than 1 percent of the time for treatment of complex stones."
100 ounces of prevention
The best treatment for kidney stones is to avoid developing them in the first place. If you've had a kidney stone in the past, you are likely to form another. That's why prevention is important. NIDDK says the therapy your doctor gives you depends on the type of stone you have. For example, a medicine that helps prevent calcium stones will not work if you have a struvite stone. The diet changes that help prevent uric acid stones may have no effect on calcium stones. Therefore, careful analysis of the stone will help guide your treatment.
The most important part of prevention is getting plenty of fluids. This dilutes the urine, which, in turn, triggers increased urination. More trips to the bathroom help remove excess chemicals from the urine and kidneys, lowering the chances of stone formation.
"In my mind, any type of fluid is going to be good for the patient--the main goal is to drink at least 100 ounces a day of whatever they like to drink," Dr. Preminger says. "Water has the advantage of being inexpensive and plentiful, so that's what we encourage them to drink."
People who form kidney stones were once told to avoid dairy products and other foods that contained a lot of calcium. Recent studies have shown that foods high in calcium actually help prevent stones, according to the NIDDK. Calcium supplements, however, may increase the risk of developing stones.
Eat less protein
For some people, decreasing the amount of protein, especially protein from meat, in their diet may help prevent stones. Protein can increase uric acid, calcium, and oxalates in the urine and reduces citrate.
People at risk for uric acid stones may benefit from decreasing their intake of foods that contain purines. These foods include sardines, yeast, and organ meats.
People who absorb an increased amount of oxalate should avoid drinking large amounts of tea, which contains high levels of oxalate. Other foods to avoid include chocolate, beets, coffee, cola, nuts, rhubarb, spinach, strawberries, and wheat bran.
Medication may be prescribed to help prevent kidney stones. The drugs control the amount of substances in the urine that form crystals (for hypercalciuria, for instance), or prevent the infections that can lead to stone growth (for struvite stones, for instance).
You should also limit your daily sodium intake. Salt is another chemical that must leave the body through the urine, and the more chemicals that are in the urine, the more likely you are to form a stone.
Are you at risk?
Conditions that may increase the chance of developing kidney stones:
A family history of stone formation
An inherited condition that causes the body to absorb too much calcium
A low level of citrate in the urine, which may contribute to calcium stones
Overactive parathyroid glands
Urinary tract infections
High blood pressure