What Causes Kidney Stones?
When substances in the urine—such as calcium, oxalate, and phosphorus—become highly concentrated, kidney stones can form. People who do not drink enough fluids may also be at higher risk, as their urine is more concentrated. Kidney stones often do not have one specific cause, although some factors may increase your risk.
Types of Kidney Stones
Identifying the type of kidney stone can help determine the cause and treatment protocol, as well as how to best reduce your risk of getting future kidney stones.
- Calcium-based stones. The most commonly found kidney stones are calcium stones, usually in the form of calcium oxalate. Oxalate is a naturally occurring substance found in some foods. In particular, some fruits, vegetables, nuts and chocolate have high oxalate content. A modification of your diet can help reduce the risk of acquiring calcium-based stones.
- Struvite stones. This type of stone is composed of magnesium ammonium phosphate and occur most often from certain types of bacteria caused by urinary tract infections. These bacteria increase the pH in urine, making it less acidic. Eating foods such as meat, dairy and grains can help increase the amount of acids produced in your body.
- Uric acid stones. Uric acid stones occur when the urine has a high acid content and and low pH, and can be caused by not drinking enough fluids, eating a high protein diet or from disorders such as gout.
- Cystine stones. This type of kidney stone results when the body abnormally processes amino acids.
Who Gets Kidney Stones? What are the Risk Factors?
Kidney stones are common. According to the most recent data from the National Institute of Diabetes and Digestive and Kidney Diseases, about 11 percent of men and 6 percent of women in the United States have kidney stones at least once during their lifetime. Men are affected more often than women, and overweight and obese people are more likely to get a kidney stone than people of normal weight.
Risk factors include:
- Gender – men are more likely than women to develop a kidney stone
- Age – older people are more affected
- Race – Caucasians are at higher risk
- Family History
- Certain medications – including, indinavir (to treat HIV), acyclovir (anti-viral), diuretics (to rid your body of water), sulfadiazine (antibiotic)
- Associated conditions – including, obesity, inflammatory bowel disease, gout, hyperparathyroidism
- Anatomic conditions – urinary obstruction, UPJ obstruction, urinary stasis
Once you have a kidney stone, you are also more likely to develop future kidney stones.
The UCLA study “Prevalence of kidney stones in the United States” published in European Urology (PDF) reported on the risk factors that make a person especially likely to develop a kidney stone.
What are the Symptoms of Kidney Stones?
Kidney Stone Symptoms
People with kidney stones may not experience symptoms until the stone moves in your kidney or into your ureter (the tube connecting your kidney and bladder), at which point you may experience one or more of these symptoms:
- Flank Pain (discomfort in your upper abdomen or back and sides)
- Hematuria (blood in your urine)
- Nausea and/or vomiting
- Urgency to urinate
- Urinating more frequently than usual
- Pain when urinating
Many people who have small stones will have them pass through the body on their own, while large stones tend to get stuck in the urinary tract. Pain is often unrelated to stone size. The smallest stones can cause the most discomfort, while large stones may sit quietly in the kidney causing only a dull ache.
How are Kidney Stones Diagnosed?
Kidney Stone Diagnosis
Diagnosing a kidney stone requires a physical exam and a medical history to be taken by a physician. Typically a urinalysis (testing of a urine sample), an abdominal x-ray, a computerized tomography (CT) scan, or an ultrasound will be done to complete the diagnosis. According to the American Urological Association, the current gold standard for confirming kidney stones is a non-contrast CT of the abdomen and pelvis. Once a stone is detected, size and location are established and are key determinants in the best management and treatment options.
How to Know If You Have a Kidney Stone
UCLA Urologist and kidney stone specialist Dr. Kymora Scotland talks about who forms kidney stones, why kidney stones cause pain, and what to expect when passing a stone.