A kidney stone is a solid piece of material that forms in a kidney when substances that are normally found in the urine become highly concentrated. A stone may stay in the kidney or travel down the urinary tract. Kidney stones vary in size and a small stone may pass on its own, causing little pain. A larger stone may get stuck along the urinary tract and can block the flow of urine, causing severe pain, nausea, vomiting or bleeding.
People with kidney stones may have pain while urinating, see blood in the urine, or feel a sharp pain in the back or lower abdomen. The pain may last for a short or long time. People may experience nausea and vomiting with the pain. However, people who have small stones that pass easily through the urinary tract may have minimal symptoms.
Kidney stones can form when substances in the urine—such as calcium, oxalate and phosphorus—become highly concentrated. Certain foods may promote stone formation in people who are susceptible. People who do not drink enough fluids may also be at higher risk, as their urine is more concentrated.
Anyone can get a kidney stone, but some people are more prone to developing one.
- Men are affected more often than women.
- Overweight and obese people are more likely to get a kidney stone than those who maintain a healthy body mass index.
- Calcium-based antacids, the protease inhibitor indinavir (Crixivan) and anti-seizure medication topiramate (Topamax) also have an increased risk of developing kidney stones.
People who are at increased risk of kidney stones are those with:
- Hypercalciuria (high calcium in the urine)
- A family history of kidney stones
- Cystic kidney diseases
- Hyperparathyroidism (high parathyroid hormone)
- Renal tubular acidosis
- Cystinuria (high cystine formation)
- Hyperoxaluria (high oxalates in the urine)
- Hyperuricosuria (high uric acid in the urine)
- Blockage of the urinary tract
- Chronic inflammation of the bowel
- A history of gastrointestinal (GI) tract surgery
Treatment for kidney stones usually depends on their size and whether they are causing pain or obstructing the urinary tract. Kidney stones may be treated by a general practitioner or by a urologist—a doctor who specializes in the urinary tract. Small stones usually pass through the urinary tract without treatment. Still, the person may need pain medication and should drink lots of fluids to help move the stone along. Pain control may consist of oral or intravenous (IV) medication, depending on the duration and severity of the pain. IV fluids may be needed if the person becomes dehydrated from vomiting or an inability to drink. A person with a larger stone, or one that blocks urine flow and causes great pain, may need more urgent treatment, such as:
- Shock wave lithotripsy: A machine called a lithotripter is used to break the stone into pieces using sound waves.
- Ureteroscopy: A ureteroscope—a long, tube-like instrument—is used to find and retrieve the stone with a small basket or to break the stone up with laser energy.
- Ureteral stenting: Urinal stenting improves the kidney’s ability to drain.
- Percutaneous nephrolithotomy: In this procedure, a wire-thin viewing instrument called a nephroscope is used to locate and remove the stone through a small incision in the side.
The first step in preventing kidney stones is to understand what is causing the stones to form. The health care provider may ask you to try to collect the kidney stone as it passes, so it can be sent to a lab for analysis. Stones that are retrieved surgically can also be sent to a lab for analysis if they are large enough fragments to analyze.
Your health care provider may ask you to collect urine for 24 hours after a stone has passed or been removed to measure daily urine volume and mineral levels. Producing small amounts of urine or having a mineral abnormality can make it more likely to form stones.
Help prevent kidney stones by making changes in your fluid intake. Depending on the type of kidney stone you have, changes in the amounts of sodium, animal protein, calcium and oxalate consumed can also help.
Drinking enough fluids each day is the best way to help prevent most types of kidney stones. Health care providers recommend you drink two to three liters of fluid a day. People with cystine stones may need to drink even more. Though water is best, other fluids may also help prevent kidney stones, including citrus drinks, such as orange juice, lime water and lemon water.