A kidney stone is a solid piece of material that forms in the kidney. It is made from substances that normally dissolve in the urine. Each year, about 1 million people in the United States get kidney stones.
Kidney stones are more common in whites than in African-Americans. They typically strike between age 20 and 50 and are more common in men than women. If you get one stone, you are more likely to get more. Repeated stone attacks can affect kidneys.
Your urinary tract is made up of your kidneys, two bean-shaped organs about the size of your fist; two narrow muscular tubes called 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 your blood. They also help your body balance certain chemicals in your blood.
Kidney stones are made up of chemicals in your urine. These include:
Stones begin as crystals that build up inside the kidney. Small crystals can pass from your body through the urine without you ever knowing about them. When the crystals grow larger and become stones, they can get stuck in the ureter and block the flow of urine. This causes 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 called a struvite, or an infection stone. It 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. Uric acid is made from purine. This is a nitrogen compound found in protein and made in your liver. Less than 3 percent of stones are made of the amino acid cystine.
Stones can be as small as a grain of sand or as large as a golf ball.
Doctors don’t really know what causes kidney stones to form. Some people are more likely to get them because of their family history. But in most cases, they are caused by having too many salts in your urine (calcium oxalate, uric acid, and cystine). Salts can build up in the kidney when you don’t have enough urine or the levels of the salts are increased. When they build up to a certain point, the salts no longer dissolve. They form crystals, instead. Normally, the urine contains chemicals (magnesium, citrate, pyrophosphate, and various proteins) and enzymes that keep crystals from forming, or from sticking to the inner surface of the kidney.
Certain conditions make it more likely that you will get kidney stones. Those conditions are:
Urinary tract infections
Metabolic disorders (such as hyperparathyroidism)
In other words, changes in the way your body uses food and drink can increase your chances of growing crystals and, in turn, kidney stones.
Kidney stones also tend to run in families.
Some rare disorders can cause kidney stones. Some of those disorders are:
Renal tubular acidosis, sometimes a hereditary disease
Cystinuria (crystals of cystine form)
Hyperoxaluria (crystals of oxalate form)
Absorptive hypercalciuria (the body takes in too much calcium from food)
Kidney stones are more common in people with high blood pressure or hyperuricosuria (a disorder of uric acid metabolism). Stones are also common in people with gout, and in those who take in 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. In addition, 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.
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.
In most cases, treatment means letting the stone pass naturally. Your health care provider 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 8 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). This treatment 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.
Percutaneous stone removal. This treatment is used or stones too large or unable to be reached with ESWL. 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. 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.
The best treatment for kidney stones is to avoid getting 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. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) says the therapy your health care provider gives you will depend 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.
If you are overweight, losing weight may help.
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.
Kidney specialists recommend that people drink at least 100 ounces of fluid every day. Their drink of choice? Water. Water is available to everyone and has the added benefit of being very inexpensive.
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.
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 fewer 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, and decrease or stop intake of alcohol. 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 or prevent the infections that can lead to stone growth.
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.
Conditions that may increase your chance of developing kidney stones are:
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
High blood pressure