Your kidneys filter chemicals for your body by removing wastes and excess fluids from the blood. Healthy kidneys maintain your body’s proper chemical balance, but certain chemicals can build up in the kidneys and form a “stone,” which may stay in the kidney or move into the urinary tract. If the stones continue to grow, they can cause intense pain as they travel through the urinary tract and out of the body.
Kidney stones are one of the most common disorders of the urinary tract. An estimated 10 percent of Americans will experience kidney stones in their lifetime. Kidney stones account for about 600,000 emergency room visits each year. Men are more likely to have kidney stones than women, while Caucasians are five times more likely to have kidney stones than African Americans. Kidney stones occur most frequently in people between 40 and 50 years of age, and the incidence tends to decline after age 50.
A kidney stone is a hard mass that develops when crystals separate from urine and build up on the inner surfaces of the kidney. Stones develop in the kidney, but they may break loose and move through the ureter, bladder or urethra. Small stones pass through with little discomfort, but if they continue to build up and grow, this can cause intense pain.
The first symptom of a kidney stone is generally sharp, cramping pain in the back and side near the kidney or in the lower abdomen. The pain begins when a stone moves into the urinary tract, causing blockage and irritation. Nausea and vomiting may occur, and the pain may spread to the groin and genital areas. As a stone grows larger or continues to move through the urinary tract, blood may appear in the urine and you may feel the need to urinate more often or experience a burning sensation while urinating. Other symptoms include fever, loss of appetite, profuse sweating, and diarrhea or constipation.
In addition to causing severe pain, a lodged stone can block the flow of urine, causing wastes to back up into the kidneys. Such a condition must be corrected swiftly, either by surgically removing the stone or by nonsurgical medical procedures that break it up and allow it to pass naturally out of the body. If immediate action is not taken, serious kidney damage and related medical problems can result.
There are several different types of kidney stones, and each type contains various combinations of chemicals. The most common type of kidney stones contains calcium combined with either oxalate or phosphate. Another type of stone, called a struvite, is caused by infection in the urinary tract. Uric acid stones and cystine stones are the least common types.
Kidney stones are most commonly caused by not drinking enough water. They can also be caused by various diseases and disorders, and are more likely to develop in people with a family history of kidney stones. Urinary tract infections, kidney disorders and metabolic disorders such as hyperparathyroidism can lead to stone formation. Also, people with rare hereditary diseases, including renal tubular acidosis, cystinuria and hyperoxaluria, can develop kidney stones.
Other causes of stone formation include hyperuricosuria, gout, excess intake of vitamins C or D and blockage of the urinary tract. Some diuretics and antacids could cause stones by increasing the amount of calcium in the urine.
Kidney stones are diagnosed through a simple medical evaluation to help your doctor find out what is causing your symptoms. A health history and physical exam may reveal signs of a stone. Then diagnostic tests will confirm the presence of a stone and help locate it in the body. Detailed metabolic tests of your blood, urine and the stone may also be performed to determine the best course of treatment.
Diagnostic tests detect infection or reveal the image of the stone. These tests include:
- Urinalysis, or urine test
- Urine culture
- Blood test
- Kidney, ureter and bladder X-ray
- Intravenous pyelogram X-ray uses dye to locate the stone
- CT scan
Metabolic tests will help the doctor determine why the stone developed and what kind of stone may form in the future. These tests include:
- Blood screen to test for chemicals, such as calcium
- 24-hour urine sample
- Stone analysis
- Provocative tests to see how your kidneys handle chemicals, such as calcium
Most kidney stones will pass through the urinary tract with plenty of water to help move them along. In fact, about 80 percent of stones pass within two days. However, in some cases, medication or other treatment may be necessary to treat kidney stones and prevent development of future stones. About half of all people who develop kidney stones will have more stones in the future, so prevention is critical. Your doctor will discuss prevention options with you after the chemical makeup of your stone is determined. Prevention may include dietary changes, such as drinking more water, and reducing the amount of protein and sodium you consume.
A doctor may prescribe certain medications to treat and prevent kidney stones. Medications that can prevent calcium stones include thiazides, potassium citrate, orthophosphate, cellulose phosphate and urease inhibitors. Medications that prevent the formation of uric acid stones are potassium citrate, sodium bicarbonate and allopurinol. Cystine stones may be prevented with penicillamine or tiopronin.
Other treatments to break up stones may be necessary if a stone causes the complete block of urine flow, extreme pain that is not controllable with medication or a urinary tract infection. These treatment options include extracorporeal shockwave lithotripsy (ESWL), percutaneous nephrolithotomy and ureteroscopy. ESWL uses sound waves that travel through the skin and body tissues until they hit the stones and break them down into particles that can easily pass through the urinary tract. Percutaneous nephrolithotomy may be used if a stone is very large or in a location that is not conducive to using ESWL. In this procedure, a needle is passed through the skin into the kidney to break up or remove the kidney stone. Ureteroscopy uses a tube called a ureteroscope that is passed through the urethra and bladder into the ureter, where the stone is then broken up and removed.
Surgery is a rare option for removing kidney stones and is generally used only when all other options have failed. During surgery, the abdomen and kidney are cut open, the stone is removed and the incisions are closed. Surgery usually requires a six- to nine-day hospital stay.