Kidney stone are hard mineral deposits that develop in the kidneys. The deposits (crystals) form into masses (called stones) that can range in size from very small to the size of a golf ball. Kidney stones can be very painful but are not life-threatening and often do not require medical intervention. As many as one million Americans are treated each year for kidney stones.  Kidney stones are most commonly seen in adult men.
- Renal calculi
Kidney stones may contain various combinations of chemicals. Approximately 80% of stones are composed of calcium oxalate (CaOx) and calcium phosphate (CaP); 10% of struvite (magnesium ammonium phosphate produced during infection with bacteria that possess the enzyme urease), 9% of uric acid (UA); and the remaining 1% are composed of cystine or ammonium acid urate or are diagnosed as drug-related stones. 
The most common type of stone contains calcium in combination with either oxalate or phosphate. These chemicals are part of a person's normal diet and make up important parts of the body, such as bones and muscles.
A less common type of stone is caused by a urinary tract infection. This type of stone is called a struvite, triple phosphate or infection stone and occur most commonly in women.
Uric acid stones
Another type of stone, uric acid stones, are a bit less common. These are formed due to high levels of uric acid in the body. High levels of uric acid maybe due to high protein diet, gout and chemotherapy.
In a rare genetic condition known as cystinuria, too much of the amino acid cystine, which does not dissolve well in urine, is voided, leading to the formation of kidney stones made of cystine. Cystine stones are rare and only affect 1:10-15,000 people.
Signs and Symptoms
- Pain is often the first symptom of a kidney stone. The pain usually begins suddenly and can be quite severe. The pain may occur in the back or side or in the lower abdomen and may spread to the groin.
- Nausea and vomiting may also occur.
- Blood may appear in the urine, making it pink or red in color.
- Frequency of urination
- Burning with urination
- Fever and chills may occur and usually signal an infection.
While certain foods may promote stone formation in people who are susceptible, scientists do not believe that eating any specific food causes stones to form in people who are not susceptible. By definition, people who make kidney stones are not producing enough urinary fluid volume but determining the exact causes in any particular individual is far more complicated. To determine the underlying chemical risk factors, a 24 hour urine along with blood tests and chemical analysis of any available stones needs to be done. The five most common findings are
- 1) Inadequate urinary volume
- 2) Inadequate urinary citrate (hypocitraturia)
- 2) Too much urinary calcium (hypercalciuria)
- 3) Too much urinary oxalate (hyperoxaluria)
- 4) Too much urinary uric acid (hyperuricosuria)
Other factors affecting the development of kidney stones include:
- A person with a family history of kidney stones may be more likely to develop stones.
- Urinary tract infections
- Kidney disorders such as cystic kidney diseases
- Certain metabolic disorders such as hyperparathyroidism and are also linked to stone formation.
- In addition, more than 70 percent of people with a rare hereditary disease called renal tubular acidosis develop kidney stones.
- Cystinuria and hyperoxaluria are two other rare, inherited metabolic disorders that often cause kidney stones. In cystinuria, too much of the amino acid cystine, which does not dissolve in urine, is voided, leading to the formation of stones made of cystine. In patients with hyperoxaluria, the body produces too much oxalate, an organic acid derived from ingested vegetables. When the urine contains more oxalate than can be dissolved, the crystals settle out and form stones.
- Hypercalciuria is often inherited, and it may be the cause of stones in more than half of patients. Calcium is absorbed from food in excess and is lost into the urine. This high level of calcium in the urine causes crystals of calcium oxalate or calcium phosphate to form in the kidneys or elsewhere in the urinary tract.
Other causes of kidney stones are:
- Hyperuricosuria, which is a disorder of uric acid metabolism
- Excess intake of vitamin D
- Certain diuretics, commonly called water pills, and calcium-based antacids may increase the risk of forming kidney stones by increasing the amount of calcium in the urine.
- Calcium oxalate stones may also form in people who have chronic inflammation of the bowel, who have had an intestinal bypass operation, or ostomy surgery. These bowel problems tend to cause a situation where oxalate is absorbed at very high levels due to a lack of normal intestinal binding. In addition, excess citrate is lost and therefore not available as a protective agent in the urine. This disorder is also known as enteric hyperoxaluria.
- As mentioned earlier, struvite stones can form in people who have had a urinary tract infection.
- People who take the protease inhibitor indinavir, a medicine used to treat HIV/AIDS, may also be at increased risk of developing kidney stones made of this medication.
Sometimes silent stones (those that do not cause symptoms) are found on incidentally on x-ray tests taken during a general health exam.
Often, kidney stones are found on an x-ray or ultrasound taken of someone who complains of blood in the urine or sudden abdominal pain. These diagnostic images give the doctor valuable information about the stone's size, shape 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 special test called a computed tomography (CT)scan or an intravenous pyelogram (IVP). The results of all these tests help determine the proper treatment. Currently, the standard evaluation for someone suspected of a possible kidney stone, is a urine test, non-contrast or "renal colic" CT scan of the abdomen and pelvis, and a KUB (which is just a plain regular X-ray of the abdomen. The KUB stands for Kidneys, Ureters and Bladder.) The value of the KUB is that it is simple, cheap, has minimal radiation exposure, clearly shows the surgical orientation and shape of the stone, and can be used to track the stone's progress without the need for the more expensive CT scan. Therefore, it is very helpful to have the KUB done at the time of the original CT scan to facilitate tracking and followup treatment of the stone.
Most kidney stones pass from the body without any intervention except oral hydration. If the stone is collected, it can be tested so that it's composition can be determined. Stones that cause lasting symptoms and/or other complications may be treated through various techniques, most of which do not involve major surgery. Also, research advances have led to a better understanding of the many factors that promote stone formation and thus better treatments for preventing stones.
Intervention may be needed to remove a kidney stone if it:
- Does not pass after a reasonable period of time (usually 30 days) or causes constant pain
- Is too large to pass on its own (usually 7 mm or larger) or is caught in a difficult place
- Causes an ongoing urinary tract infection
- Damages kidney tissue or causes constant bleeding
- Has grown larger, as seen on follow-up x rays
- Blocks a solitary kidney
Until 20 years ago, open surgery was necessary to remove a stone. Such surgery required a recovery time of 4 to 6 weeks. Today, treatment for these stones is greatly improved, and most options do not require major open surgery and can be performed in an outpatient setting.
Extracorporeal shock wave lithotripsy (ESWL)
Extracorporeal shock wave lithotripsy is the most frequently used procedure for the treatment of kidney stones. In ESWL, shock waves that are created outside the body travel through the skin and body tissues until they hit the denser stones. The stones break down into small particles and are easily passed through the urinary tract in the urine.
Several types of ESWL devices exist. Most devices use either x rays to allow the surgeon to pinpoint the stone during treatment.In most cases, ESWL is be done on an outpatient basis. Recovery time is relatively short, and most people can resume normal activities in a few days.
Occasionally, the shattered stone particles cause blockages as they pass through the urinary tract and cause discomfort. In some cases, the doctor will insert a small tube called a stent through the bladder into the ureter to help the fragments pass and prevent clogging. Sometimes the stone is not completely shattered with one treatment, and additional treatments may be needed.
Sometimes a procedure called percutaneous nephrolithotomy is recommended to remove a stone. This treatment is often used when the stone is quite large or in a location that does not allow effective use of ESWL.
In this procedure, the surgeon makes a tiny incision in the back and creates a tunnel directly into the kidney. Using an instrument called a nephroscope, the surgeon locates and removes the stone. For large stones, some type of energy probe—ultrasonic or electrohydraulic—may be needed to break the stone into small pieces. Often, patients stay in the hospital for several days and may have a small tube called a nephrostomy tube left in the kidney during the healing process.
One advantage of percutaneous nephrolithotomy is that the surgeon can remove some of the stone fragments directly instead of relying solely on their natural passage from the kidney.
Ureteroscopic Stone Removal
Although stones in the ureters can be treated with ESWL, ureteroscopy is another option especially for mid- and lower-ureter stones. No incision is made in this procedure. Instead, the urologist passes a small fiberoptic instrument called a ureteroscope through the urethra and bladder into the ureter. The surgeon then locates the stone and either removes it with a cage-like device (basket) or shatters it with a laser or similar probe. A small tube or stent may be left in the ureter for a few days to help urine flow and prevent pain from ureteral spasm.
Before fiber optics made ureteroscopy possible, physicians used a similar “blind basket” extraction method. This "blind" technique is rarely used now because of the higher risks of damage to the ureters and the improved outcomes when ureteroscopy is used. Ureteroscopy is a relatively demanding surgery, so if it is preferred by your urologist be sure to ask his success rate and experience level with this instrument.
A person who has had a kidney stone is likely to form another, and steps are taken towards prevention. To help determine the cause, the doctor will order laboratory tests, including 24 hour urine and blood tests and take a medical history including eating habits and medications. Risk factors increasing the likelihood of kidney stones are identified and then modified. Fluid intake is also encouraged. If a stone has been removed, or if the patient has passed a stone and saved it, a stone analysis by the laboratory will aid in the diagnostic process. With this information, the physician can indicate which foods, beverages or medication changes will be needed to reduce the risk of recurrence.
Kidney stone disease cannot be completely cured, but the recurrence rate can be drastically reduced with a full diagnostic preventive analysis. Ultimately, the success of such evaluations will depend on the willingness of the patient to follow through on treatment even though there is no obvious or discernible difference whether the patient follows therapy or not. The only difference is the risk of creating new stones. If treatment is abandoned, then the risk increases accordingly.
The patient will be asked to collect urine for 24 hours after a stone has passed or been removed. For a 24-hour urine collection, the patient is given a large container, which is to be refrigerated between trips to the bathroom. The collection is used to measure urine volume and levels of acidity, calcium, sodium, uric acid, phosphate, sulfate, oxalate, citrate, and creatinine (a product of muscle metabolism). The doctor will use this information to determine the cause of the stone. A second 24-hour urine collection several months later may be requested to determine whether the prescribed treatment is working and to make further adjustments.
A simple and most important lifestyle change to prevent stones is to drink more liquids—water is best. In general, someone who tends to form stones should try to drink enough liquids throughout the day to produce at least 2 quarts of urine in every 24-hour period.
In the past, people who formed calcium stones were told to avoid dairy products and other foods with high calcium content. Recent studies have shown that a reasonable intake of foods high in calcium, including dairy products, may actually help prevent calcium stones . Taking calcium in excess, however, may increase the risk of developing stones.
Someone who has highly acidic urine or with high urinary uric acid levels may need to eat less meat, fish, and poultry. These foods increase the amount of acid and uric acid in the urine.
To prevent cystine stones, a person should drink enough water each day to dilute the concentration of cystine that escapes into the urine, which may be difficult. More than a gallon of water may be needed every 24 hours, and a third of that must be drunk during the night. The goal with cystine stones is to drink sufficient water to make at least 3 liters of urine a day or more.
People prone to forming calcium oxalate stones may be asked to limit or avoid certain foods if their urine contains an excess of oxalate. These high-oxalate foods include:
- Swiss chard
- Wheat germ
- Soybean crackers
- Black Indian tea
- Sweet potatoes
Foods that have medium amounts of oxalate may be eaten in limited amounts. These foods include:
- Green pepper
- Red raspberries
- Fruit cake
- A doctor may prescribe certain medications to help prevent calcium and uric acid stones. These medicines control the amount of acid or alkali in the urine, key factors in crystal formation. The medicine allopurinol may also be useful in some cases of hyperuricosuria.
- Doctors usually try to control hypercalciuria, and thus prevent calcium stones, by prescribing certain diuretics, such as hydrochlorothiazide. These medicines decrease the amount of calcium released by the kidneys into the urine by favoring calcium retention in bone. They work best when sodium intake is low.
- Rarely, patients with hypercalciuria are given the medicine sodium cellulose phosphate, which binds calcium in the intestines and prevents it from leaking into the urine.
- If cystine stones cannot be controlled by drinking more fluids, a doctor may prescribe medicines such as Thiola and Cuprimine, which help reduce the amount of cystine in the urine.
- For struvite stones that have been totally removed, the first line of prevention is to keep the urine free of bacteria that can cause infection. A patient's urine will be tested regularly to ensure no bacteria are present.
- If struvite stones cannot be removed, a doctor may prescribe a medicine called acetohydroxamic acid (AHA). AHA is used with long-term antibiotic medicines to prevent the infections that lead to stone growth.
- People with hyperparathyroidism sometimes develop calcium stones. Treatment in these cases is usually surgery to remove the abnormal parathyroid glands, which are located in the neck. In most cases, only one of the glands is abnormally enlarged. Removing the glands cures the patient's problem with hyperparathyroidism and kidney stones.
Chances of Developing Kidney Stones
For unknown reasons, 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 percent of the population had stone-forming disease. By the early 1990s, the portion of the population with the disease had increased to more than 5 percent.  Caucasians are more prone to develop kidney stones than African Americans. Stones occur more frequently in men. The prevalence of kidney stones rises dramatically as men enter their 40s and continues to rise into their 70s. For women, the prevalence of kidney stones peaks in their 50s. Once a person gets more than one stone, other stones are likely to develop.
- There appears to be a relationship between hypertension (high blood pressure) and the excretion of urinary acid and formation of kidney stones. 
- Shock wave lithotripsy was shown to be effective in the treatment of 89.5% of kidney stones in a recent study from the Kingdom of Saudi Arabia. 
- Percutaneous nephrolithotomy appears to be the best method for treating kidney stones in transplanted kidneys. 
- Kidney stones containing large amounts of calcium and phospate are more likely to recur after percutaneous nephrolithotomy. Further studies to determine the cause of the increased frequency of recurrence as well as to evaluate other treatment methods for recurent are warranted. 
- The topical administration of drugs intended to decrease the renal pressure during endoscopic treatment of kidney stones is being studied. 
- The effect of sports drinks on the tendency to form kidney stones is being evaluated for the first time. 
About 5% of American women and 12% of men will develop a kidney stone at some time in their life, and prevalence has been rising in both sexes. 
- ↑ National Kidney Foundation. Kidney Stones
- ↑ 2.0 2.1 Coe FL, Evan A, Worcester E. Kidney stone disease. J Clin Invest. 2005 Oct;115(10):2598-608. Abstract
- ↑ National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC). Kidney Stones in Adults
- ↑ Losito A, Nunzi EG, Covarelli C, Nunzi E, Ferrara G. Increased acid excretion in kidney stone formers with essential hypertension. Nephrol Dial Transplant. 2008 Aug 20. [Epub ahead of print] Abstract
- ↑ Tayib AM, Mosli HA, Farsi HM, Atwa MA, Saada HA. Shock wave lithotripsy in patients with renal calculi. Saudi Med J. 2008 Aug;29(8):1180-3. Abstract
- ↑ Rifaioglu MM, Berger AD, Pengune W, Stoller ML. Percutaneous Management of Stones in Transplanted Kidneys. Urology. 2008 Jul 22. [Epub ahead of print] Abstract
- ↑ Kacker R, Meeks JJ, Zhao L, Nadler RB. Decreased stone-free rates after percutaneous nephrolithotomy for high calcium phosphate composition kidney stones. J Urol. 2008 Sep;180(3):958-60; discussion 960. Epub 2008 Jul 17. Abstract
- ↑ ClinicalTrials.gov. Retrograde Intrarenal Stone Surgery - A Method of Treating the ESWL Resistant Kidney Stone
- ↑ ClinicalTrials.gov. The Effects of Sports Drinks on Urinary Lithogenicity