What are kidney stones?
A kidney stone is a hard, crystalline mineral material formed within the kidney or urinary tract. Kidney stones are a common cause of blood in the urine (hematuria) and often severe pain in the abdomen, flank, or groin.
Kidney stones are sometimes called renal calculi. The condition of having kidney stones is termed nephrolithiasis. Having stones at any location in the urinary tract is referred to as urolithiasis, and the term ureterolithiasis is used to refer to stones located in the ureters.
Types of kidney stones
Not all kidney stones are made up of the same crystals. The different types of kidney stones include:
Calcium stones are the most common. They’re often made of calcium oxalate (though they can consist of calcium phosphate or maleate). Eating fewer oxalate-rich foods can reduce your risk of developing this type of stone. High-oxalate foods include:
- potato chips
However, even though some kidney stones are made of calcium, getting enough calcium in your diet can prevent stones from forming.
This type of kidney stone is more common in men than in women. They can occur in people with gout or those going through chemotherapy.
This type of stone develops when urine is too acidic. A diet rich in purines can increase urine’s acidic level. Purine is a colorless substance in animal proteins, such as fish, shellfish, and meats.
This type of stone is found mostly in women with urinary tract infections (UTIs). These stones can be large and cause urinary obstruction. They result from a kidney infection. Treating an underlying infection can prevent the development of struvite stones.
Cystine stones are rare. They occur in both men and women who have the genetic disorder cystinuria. With this type of stone, cystine — an acid that occurs naturally in the body — leaks from the kidneys into the urine.
Causes of Kidney Stones
The leading cause of kidney stones is a lack of water in the body.
Stones are more commonly found in individuals who drink less than the recommended eight to ten glasses of water a day.
When there is not enough water to dilute the uric acid, a component of urine, the urine becomes more acidic.
An excessively acidic environment in urine can lead to the formation of kidney stones.
Medical conditions such as Crohn’s disease, urinary tract infections, renal tubular acidosis, hyperparathyroidism, medullary sponge kidney, and Dent’s disease increase the risk of kidney stones.
Risk factors for kidney stones
The greatest risk factor for kidney stones is making less than 1 liter of urine per day. This is why kidney stones are common in premature infants who have kidney problems. However, kidney stones are most likely to occur in people between the ages of 20 and 50.
Different factors can increase your risk of developing a stone. In the United States, white people are more likely to have kidney stones than black people.
Sex also plays a role. More men than women develop kidney stones, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
A history of kidney stones can increase your risk. So does a family history of kidney stones.
Other risk factors include:
- a diet with high levels of protein, salt, or glucose
- hyperparathyroid condition
- gastric bypass surgery
- inflammatory bowel diseases that increase calcium absorption
- taking medications such as triamterene diuretics, antiseizure drugs, and calcium-based antacids
Symptoms of Kidney Stones
A kidney stone may not cause symptoms until it moves around within your kidney or passes into your ureter — the tube connecting the kidney and bladder. At that point, you may experience these signs and symptoms:
- Severe pain in the side and back, below the ribs
- Pain that radiates to the lower abdomen and groin
- Pain that comes in waves and fluctuates in intensity
- Pain on urination
- Pink, red or brown urine
- Cloudy or foul-smelling urine
- Nausea and vomiting
- Persistent need to urinate
- Urinating more often than usual
- Fever and chills if an infection is present
- Urinating small amounts
Pain caused by a kidney stone may change — for instance, shifting to a different location or increasing in intensity — as the stone moves through your urinary tract.
Kidney stones that remain inside the body can also lead to many complications, including blockage of the tube connecting the kidney to the bladder, which obstructs the path that urine uses to leave the body.
According to research, people with kidney stones have a significantly higher risk of developing chronic kidney disease.
Diagnosis of Kidney Stones
If your doctor suspects you have a kidney stone, you may have diagnostic tests and procedures, such as:
- Blood testing. Blood tests may reveal too much calcium or uric acid in your blood. Blood test results help monitor the health of your kidneys and may lead your doctor to check for other medical conditions.
- Urine testing. The 24-hour urine collection test may show that you’re excreting too many stone-forming minerals or too few stone-preventing substances. For this test, your doctor may request that you perform two urine collections over two consecutive days.
- Imaging. Imaging tests may show kidney stones in your urinary tract. Options range from simple abdominal X-rays, which can miss small kidney stones, to high-speed or dual energy computerized tomography (CT) that may reveal even tiny stones. Other imaging options include an ultrasound, a noninvasive test, and intravenous urography, which involves injecting dye into an arm vein and taking X-rays (intravenous pyelogram) or obtaining CT images (CT urogram) as the dye travels through your kidneys and bladder.
- Analysis of passed stones. You may be asked to urinate through a strainer to catch stones that you pass. Lab analysis will reveal the makeup of your kidney stones. Your doctor uses this information to determine what’s causing your kidney stones and to form a plan to prevent more kidney stones.
Treatment of Kidney Stones
Treatment for kidney stones varies, depending on the type of stone and the cause.
Small stones with minimal symptoms
Most small kidney stones won’t require invasive treatment. You may be able to pass a small stone by:
- Drinking water. Drinking as much as 2 to 3 quarts (1.9 to 2.8 liters) a day may help flush out your urinary system. Unless your doctor tells you otherwise, drink enough fluid — mostly water — to produce clear or nearly clear urine.
- Pain relievers. Passing a small stone can cause some discomfort. To relieve mild pain, your doctor may recommend pain relievers such as ibuprofen (Advil, Motrin IB, others), acetaminophen (Tylenol, others) or naproxen sodium (Aleve).
- Medical therapy. Your doctor may give you a medication to help pass your kidney stone. This type of medication, known as an alpha-blocker, relaxes the muscles in your ureter, helping you pass the kidney stone more quickly and with less pain.
Large stones and those that cause symptoms
Kidney stones that can’t be treated with conservative measures — either because they’re too large to pass on their own or because they cause bleeding, kidney damage or ongoing urinary tract infections — may require more-extensive treatment. Procedures may include:
- Using sound waves to break up stones. For certain kidney stones — depending on size and location — your doctor may recommend a procedure called extracorporeal shock wave lithotripsy (ESWL).ESWL uses sound waves to create strong vibrations (shock waves) that break the stones into tiny pieces that can be passed in your urine. The procedure lasts about 45 to 60 minutes and can cause moderate pain, so you may be under sedation or light anesthesia to make you comfortable.ESWL can cause blood in the urine, bruising on the back or abdomen, bleeding around the kidney and other adjacent organs, and discomfort as the stone fragments pass through the urinary tract.
- Surgery to remove very large stones in the kidney. A procedure called percutaneous nephrolithotomy (nef-row-lih-THOT-uh-me) involves surgically removing a kidney stone using small telescopes and instruments inserted through a small incision in your back.You will receive general anesthesia during the surgery and be in the hospital for one to two days while you recover. Your doctor may recommend this surgery if ESWL was unsuccessful.
- Using a scope to remove stones. To remove a smaller stone in your ureter or kidney, your doctor may pass a thin lighted tube (ureteroscope) equipped with a camera through your urethra and bladder to your ureter.Once the stone is located, special tools can snare the stone or break it into pieces that will pass in your urine. Your doctor may then place a small tube (stent) in the ureter to relieve swelling and promote healing. You may need general or local anesthesia during this procedure.
- Parathyroid gland surgery. Some calcium phosphate stones are caused by overactive parathyroid glands, which are located on the four corners of your thyroid gland, just below your Adam’s apple. When these glands produce too much parathyroid hormone (hyperparathyroidism), your calcium levels can become too high and kidney stones may form as a result.Hyperparathyroidism sometimes occurs when a small, benign tumor forms in one of your parathyroid glands or you develop another condition that leads these glands to produce more parathyroid hormone. Removing the growth from the gland stops the formation of kidney stones. Or your doctor may recommend treatment of the condition that’s causing your parathyroid gland to overproduce the hormone.
Prevention of Kidney Stones
Prevention of kidney stones may include a combination of lifestyle changes and medications.
You may reduce your risk of kidney stones if you:
- Drink water throughout the day. For people with a history of kidney stones, doctors usually recommend passing about 2.6 quarts (2.5 liters) of urine a day. Your doctor may ask that you measure your urine output to make sure that you’re drinking enough water.If you live in a hot, dry climate or you exercise frequently, you may need to drink even more water to produce enough urine. If your urine is light and clear, you’re likely drinking enough water.
- Eat fewer oxalate-rich foods. If you tend to form calcium oxalate stones, your doctor may recommend restricting foods rich in oxalates. These include rhubarb, beets, okra, spinach, Swiss chard, sweet potatoes, nuts, tea, chocolate and soy products.
- Choose a diet low in salt and animal protein. Reduce the amount of salt you eat and choose nonanimal protein sources, such as legumes. Consider using a salt substitute, such as Mrs. Dash.
- Continue eating calcium-rich foods, but use caution with calcium supplements. Calcium in food doesn’t have an effect on your risk of kidney stones. Continue eating calcium-rich foods unless your doctor advises otherwise.Ask your doctor before taking calcium supplements, as these have been linked to an increased risk of kidney stones. You may reduce the risk by taking supplements with meals. Diets low in calcium can increase kidney stone formation in some people.
Ask your doctor for a referral to a dietitian who can help you develop an eating plan that reduces your risk of kidney stones.
Medications for Kidney Stones
Medications can control the number of minerals and salts in your urine and may be helpful in people who form certain kinds of stones. The type of medication your doctor prescribes will depend on the kind of kidney stones you have. Here are some examples:
- Calcium stones. To help prevent calcium stones from forming, your doctor may prescribe a thiazide diuretic or a phosphate-containing preparation.
- Uric acid stones. Your doctor may prescribe allopurinol (Zyloprim, Aloprim) to reduce uric acid levels in your blood and urine and a medicine to keep your urine alkaline. In some cases, allopurinol and an alkalizing agent may dissolve the uric acid stones.
- Struvite stones. To prevent struvite stones, your doctor may recommend strategies to keep your urine free of bacteria that cause infection. Long-term use of antibiotics in small doses may help achieve this goal. For instance, your doctor may recommend an antibiotic before and for a while after surgery to treat your kidney stones.
- Cystine stones. Cystine stones can be difficult to treat. Your doctor may recommend that you drink more fluids so that you produce a lot more urine. If that alone doesn’t help, your doctor may also prescribe a medication that decreases the amount of cystine in your urine.
When to see a doctor
Make an appointment with your doctor if you have any signs and symptoms that worry you.
Seek immediate medical attention if you experience:
- Pain so severe that you can’t sit still or find a comfortable position
- Pain accompanied by nausea and vomiting
- Pain accompanied by fever and chills
- Blood in your urine
- Difficulty passing urine
What to expect from your doctor
Your doctor is likely to ask you a number of questions, such as:
- When did your symptoms begin?
- Have your symptoms been continuous or occasional?
- How severe are your symptoms?
- What, if anything, seems to improve your symptoms?
- What, if anything, appears to worsen your symptoms?
- Has anyone else in your family had kidney stones?
For kidney stones, some basic questions include:
- Do I have a kidney stone?
- What size is the kidney stone?
- Where is the kidney stone located?
- What type of kidney stones do I have?
- Will I need medication to treat my condition?
- Will I need surgery or another procedure?
- What’s the chance that I’ll develop another kidney stone?
- How can I prevent kidney stones in the future?
- I have other health conditions. How can I best manage them together?
- Do I need to follow any restrictions?
- Should I see a specialist? If so, does insurance typically cover the services of a specialist?
- Is there a generic alternative to the medicine you’re prescribing?
- Do you have any educational material that I can take with me? What websites do you recommend?
- Do I need a follow-up visit?
Frequently Asked Questions About Kidney Stones
What is a kidney stone?
A kidney stone is a hard object that is made from chemicals in the urine. Urine has various wastes dissolved in it. When there is too much waste in too little liquid, crystals begin to form. The crystals attract other elements and join together to form a solid that will get larger unless it is passed out of the body with the urine. The stone-forming chemicals are calcium, oxalate, urate, cystine, xanthine, and phosphate.
Usually, these chemicals are eliminated in the urine by the body’s master chemist: the kidney. In most people, having enough liquid washes them out or other chemicals in urine stop a stone from forming.
After it is formed, the stone may stay in the kidney or travel down the urinary tract into the ureter. Sometimes, tiny stones move through the body in the urine without causing too much pain. But stones that don’t move may cause a back-up of urine in the kidney, ureter, the bladder or the urethra. This is what causes the pain.
What causes kidney stones to form?
Possible causes include drinking too little water, exercise (too much or too little), obesity, weight loss surgery or eating food with too much salt or sugar. Infections and family history might be important in some people. Eating too much fructose correlates with an increased risk of developing a kidney stone. Fructose can be found in table sugar and high fructose corn syrup. In some individuals, fructose can be metabolized into oxalate.
How common are kidney stones?
Each year, more than half a million people go to emergency rooms for kidney stone problems. lt is thought that one in ten people will have a kidney stone at some time in their lives.
The number of people in the United States with kidney stones has been increasing over the past 30 years. In the late 1970s, less than 4% of the population had had kidney stones; by the early 1990s, more than 5%. The rates are continuing to increase.
The peak age for stones is between 20 years and 50 years. White Americans are more prone to develop kidney stones than African Americans, and men are much more likely to develop stones than women. Other diseases like high blood pressure, diabetes, obesity, osteoporosis, chronic diarrhea, or kidney cysts might increase the risk of stones. Diabetes increases the risk of developing kidney stones, especially in younger women.
Only about 25% of kidney stones occur in people with a family history of stones. After bariatric (weight loss) surgery, in which the digestive tract is altered, kidney stones are more common as levels of oxalate are much higher after this surgery.
What are the symptoms of a kidney stone?
Some kidney stones are as small as a grain of sand. Others are as large as a pebble. A few are as large as a golf ball! As a general rule, the larger the stone, the more noticeable are the symptoms.
The symptoms could be one or more of the following:
- severe pain on either side of your lower back
- vague pain or stomach ache that doesn’t go away
- blood in the urine
- nausea or vomiting
- fever and chills
- urine that smells bad or looks cloudy
The kidney stone starts to hurt when it causes irritation or blockage. This builds rapidly to extreme pain. In most cases, kidney stones pass without causing damage, but they usually cause a lot of pain. Pain relievers may be the only treatment needed for small stones. Other treatments may be needed, especially for those stones that cause lasting symptoms or other complications. In severe cases, however, surgery may be required.
How are stones diagnosed?
Diagnosis of kidney stone starts with a medical history, physical examination, and imaging tests. Your doctors will want to know the exact size and shape of the kidney stones. This can be done with a high-resolution CT scan from the kidneys down to the bladder or an x-ray called a “KUB x-ray” (kidney-ureter-bladder x-ray) which will show the size of the stone and its position.
The KUB x-ray is often obtained by the surgeons to determine if the stone is suitable for shock wave treatment. The KUB test may be used to monitor your stone before and after treatment, but the CT scan is usually preferred for diagnosis.
In some people, doctors will also order an intravenous pyelogram or IVP, a special type of X-ray of the urinary system that is taken after injecting a dye.
Why does the doctor need to examine the contents of the stone?
There are four types of stones. Studying the stone can help understand why you have it and how to reduce the risk of further stones. The most common type of stone contains calcium. Calcium is a normal part of a healthy diet. The kidney usually removes extra calcium that the body doesn’t need.
Often people with stones keep too much calcium. This calcium combines with waste products like oxylate to form a stone. The most common combination is called calcium oxalate. Less common types of stones are infection-related stones, containing magnesium and ammonia called struvite stones and acid-related stones, called uric acid stones, which might be related to eating too much protein. The rarest type of stone is a cystine stone that tends to run in families.
How are kidney stones treated?
You may be asked to drink a lot of water. Doctors try to let the stone pass without surgery. But if it is too large, if it blocks the flow of urine, or if there is a sign of infection, it is removed with surgery.
Shock-wave lithotripsy is a noninvasive procedure that uses high-energy sound waves to blast the stones into fragments that are then more easily passed out in the urine. In ureteroscopy, an endoscope is inserted through the ureter to retrieve or obliterate the stone. Rarely, for very large or complicated stones, doctors will use percutaneous nephrolithotomy/nephrolithotripsy.
Are there any long term consequences of having a kidney stone?
Kidney stones increase the risk of developing chronic kidney disease. If you have had one stone, you are at an increased risk of having another stone. Those who have developed one stone are at approximately 50% risk for developing another within 5 to 7 years.
What can I do to decrease my risk of having kidney stones?
Drinking enough fluid will help keep your urine less concentrated with waste products. Darker urine is more concentrated, so your urine should appear very light yellow to clear if you are well hydrated. Most of the fluid you drink should be water.
Water is better than soda, sports drinks or coffee/tea. If you exercise or if it is hot outside, you should drink more. Sugar and high-fructose corn syrup should be limited to small quantities. You can reduce excess salt in your diet and, if overweight, try to get to a normal weight.
Keep in mind, high-protein weight-loss diets can add to the stone risk. Protein is found in beef, chicken, pork, fish, milk, and eggs. You need protein (50 grams a day), but it needs to be part of a balanced diet. Some herbal substances are promoted as helping prevent stones. You should know that there is insufficient published medical evidence to support the use of any herb or supplement in preventing stones.
See your doctor and/or a registered dietitian about making diet changes if you have had a stone or think you could be at increased risk for getting a kidney stone. To guide you, they need to know your medical history and the food you eat. Here are some questions you might ask:
- What food may cause kidney stones?
- Should I take vitamin and mineral supplements?
- What beverages are good choices for me?
Do children get kidney stones?
Kidney stones are found in children as young as 5 years. In fact, this problem is so common in children that some hospitals conduct ‘stone’ clinics for pediatric patients. The increase in the United States has been attributed to several factors, mostly related to food choices.
The two most important reasons are not drinking enough fluids and eating foods that are high in salt. Kids should eat less salty potato chips and French fries. There are other salty foods: sandwich meats; canned soups; packaged meals; and even sports drinks. Sodas can also increase the risk of stones due to the high sucrose content (a kind of sugar).
Drinking water is important, but how do you get kids to drink more water? Parents can send a water bottle with lunch to school, instead of a juice box or sports drink. Make a habit when they are very young to serve water with every meal and snack.
Kids like ice water, especially when the ice is made in a tray of shapes (like stars or hearts). Don’t wait for your child to tell you he or she is thirsty. They may not realize it. Bring water to sports activities and to the park. Have a water bottle in the car on every trip.
In some children, being overweight adds to the risk. In others, being very active in sports and not drinking water adds to the risk. In still others, regularly eating foods high in salt adds to the risk. Encourage your kids to drink milk and eat yogurt. Dairy products help because calcium binds with oxalate before it gets into the kidneys.
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