The urinary tract is the body’s drainage system for removing wastes and extra water. It includes two kidneys, two ureters, a bladder, and a urethra. The kidneys are two bean-shaped organs, each about the size of a fist. Every day, they process about 190 liters of blood to produce about 0.945-1.90 ml of urine.

Urolithiasis refers to the presence of calculi anywhere along the course of the urinary tracts. The terms urolithiasis, nephrolithiasis and renal or urinary tract stones are used interchangeably, although there are slightly varying definitions of each (nephrolithiasis refers to calculi in the kidneys). Because these cases share most of the disease process, they are often discussed in conjunction.

A urinary tract stone or calculus is one of the most common disorders of the renal system. A solid piece of material that forms in a kidney, ureter or bladder when substances that are normally found in the urine become highly concentrated due to dehydration and poor diet. A stone may stay in the kidney or travel down the urinary tract.

Most urinary tract stones are small enough to be passed out in the urine without any complication. However, some stones are large to amount that require treatment. The most important aspect of medical therapy is maintaining a high fluid intake and subsequent high urinary volume.

Urolithiasis is the medical term used to describe stones occurring in the urinary tract, primarily in the kidney (nephrolithiasis) or ureter (ureterolithiasis), and may also form in or migrate into the lower urinary system (bladder or urethra). The result are small, hard mineral deposits that may stay in the tract or pass through the urine, based on its size and hydration status.

• Calcium stones: the most common type of urinary tract stone and occur in two major forms: calcium oxalate and calcium phosphate. Calcium oxalate stones are more common and may be caused by high calcium and high oxalate excretion. Oxalate is a naturally occurring substance found in some food like spinach and chocolate. Dietary factors, high doses of vitamin D, intestinal bypass surgery and several metabolic disorders can increase the concentration of calcium or oxalate in urine. Calcium phosphate stones are caused by the combination of high urine calcium and alkaline urine, meaning the urine has a high pH level.
• Uric acid stones: form when the urine is persistently acidic. A diet rich in purines - substances found in animal protein such as meats, fish, and shellfish - may increase uric acid in urine. If uric acid becomes concentrated in the urine, it can settle and form a stone by itself or along with calcium. Genetic factors and gout disease may have a participation in this condition.
• Struvite stones: Usually associated by urinary tract infections which change the urinary environment to permit rapid stone growth. These stones can grow quickly and become quite large, sometimes with few symptoms or little warning.
• Cystine stones: These rare calculi form in people with a hereditary disorder that causes the kidneys to excrete too much of certain amino acid called cystine due to an inherited defect in its transport within the kidney. Patients who are affected tend to be young and develop recurrent urinary tract stones throughout life.

Urinary tract stones form when the urine contains more crystal-forming substances - such as calcium, oxalate, uric acid and phosphorus - than the fluid in the urine can dilute. At the same time, the urine may lack substances that prevent crystals from sticking together, such as nephrocalcin and uropontin, creating an ideal environment for the stones to scheme.

• Dehydration. The single most important determinant of stone formation is low fluid intake. People who live in warm climates and those who sweat a lot may be at higher risk;
• Obesity. High body mass index (BMI) and large waist size have been linked to an increased risk of urinary tract stones;
• Certain foods and drinks. Eating a diet that's high in protein, sodium and oxalate may increase the risk of some types of urinary tract stones;
• Digestive diseases and surgeries. Gastric bypass surgery, inflammatory bowel disease or chronic diarrhea can cause digestive changes that affect absorption of calcium and water;
• Hyperparathyroidism. In this condition, the parathyroid glands, which are four pea-sized glands located in the neck, release too much hormone, causing extra calcium in the blood that will be secreted in urine;
• Hypercalciuria. A condition that runs in families in which urine contains unusually large amounts of calcium; this is the most common condition found in those who form calcium stones;
• Taking certain medications. These include: calcium-based antacids, Indinavir (a medication used to treat HIV infection) and Topiramate (anti-seizure medication);
• Medical and family history. Having a first relative with this problem increases its chances. Also having more than one urinary tract stone will hasten the risk for forming another;
• Polycystic kidney disease. An inherited disorder that cause clusters of fluid-filled sacs to form on the kidneys causing them to become enlarged and could lead to hypertension and renal failure;
• hyperuricosuria. A high concentration of uric acid in the urine due to either excess dietary intake of purine-rich foods or endogenous uric acid overproduction. Gout disease that characterized severe joint pain also increases the risk;
• Renal tubular acidosis. A disease that occurs when the kidneys fail to excrete acids into the urine, which causes a person’s blood to remain too acidic;
• Cystinuria. A rare, inherited condition in which urine contains high levels of the amino acid cysteine;
• Hyperoxaluria. In this condition, urine contains unusually large amounts of oxalate;
• Calcium supplements: Calcium in food doesn't have an effect on the risk of urinary tract stones, but supplements may be linked to this problem. Taking these supplement with food will decrease that risk.

A low fluid intake with a subsequent low volume of urine production, produce high concentrations of stone-forming solutes in the urine. When the chemical concentration levels reach the point at which they no longer dissolve, these substances form crystals that may fix to surfaces of renal filtering and passing structures, thus creating the nidus for subsequent stone growth. Urothelial injury and repair after a stone episode may increase surface expression of these molecules to favor further crystal adhesion, which may increase the chances of recurrence.

A urinary tract stone may not cause symptoms until it moves around within the kidney or passes into the ureter. Pain is the major symptom of urinary tract stone. This pain could be:

• Back or side pain that won’t go away, or felt few hours in different regions;
• starts to travel down to the lower abdomen and groin;
• Aggravated with urination and certain foods or drinks.

Other symptoms for urinary tract stones rather than pain may include:

• 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.

• Blood testing. The blood test can show biochemical problems that can lead to urinary tract stones. It may reveal too much calcium or uric acid in the blood. The results will help monitor the health of kidneys and may lead the doctor to check for other medical conditions;
• Urine testing. The 24-hour urine collection test may show excreting too many stone-forming minerals or too few stone-preventing substances. For this test, the doctor may request to perform two urine collections over two consecutive days. It could also show whether the person has an infection;
• Imaging. Imaging tests may show urinary tract stones in the urinary tract. Options range from simple abdominal X-rays, which can miss small urinary tract stones, to high-speed or dual energy computerized tomography (CT) that may reveal even tiny stones. These two imagining procedures may be done with injecting dye into a vein and taking X-rays (intravenous pyelogram) or obtaining CT images (CT urogram) as the dye travels through the kidneys and bladder;
• Analysis of passed stones. The person may be asked to urinate through a strainer to catch stones that will pass. Lab analysis will reveal the kind of calculi and the possible underlying cause and subsequently the best treatment.

Most urinary tract stones eventually pass out of the body during urination. But some can grow large enough to begin blocking the flow of urine and cause severe discomfort. Treatment for urinary tract stones usually depends on their size and what they are made of, as well as whether they are causing pain or obstructing the urinary tract. The ureter is the smallest diameter structure of the urinary tract and is the area most prone to obstruction. The consequence of stone is determined in this chart:

• Small stones: Most urinary tract stones won't require invasive treatment as they are not large enough to cause block of urine passage or severe pain. They can be eliminated by:
  • Drinking water. Drinking enough fluids is the most important guideline for people with any type of urinary tract stones. Patients with calcium or uric acid stones should drink at least 10 cups of fluid each day (at least half should be water). Those with cystine stones needs up to 16 cups;
  • Pain relievers. Passing a small stone can cause some discomfort. To relieve mild pain, the doctor may recommend analgesics such as ibuprofen, acetaminophen, or naproxen;
  • Medical therapy. The doctor may give a medication known as an alpha blocker to help pass the stone. This type of medication relaxes the muscles in the ureter, helping pass the urinary tract stone more quickly and with less pain.

• Large stones: If a stone is too big to be passed naturally through the urinary tract there may be a need for treatment to remove it or facilitate that. Available treatments include:
  • Shock wave lithotripsy. A machine called a lithotripter is used to crush the urinary tract stone. The procedure is performed by a urologist on an outpatient basis and anesthesia is used. The lithotripter generates shock waves that pass through the person’s body to break the urinary tract stone into smaller pieces to pass more readily through the urinary tract;
  • Ureteroscopy. A long, tube-like instrument with an eyepiece is used to find and retrieve the stone with a small basket or to break the stone up with laser energy. The procedure is performed by a urologist in a hospital with anesthesia. The urologist inserts the ureteroscope into the person’s urethra and slides the scope through the bladder and into the ureter;
  • Percutaneous nephrolithotomy. In this procedure, a wire-thin viewing instrument called a nephroscope is used to locate and remove the stone. The procedure is performed by a urologist in a hospital with anesthesia. During the procedure, a tube is inserted directly into the kidney through a small incision in the person’s back. For large stones, an ultrasonic probe may be needed to deliver shock waves that break the stone into small pieces.

• Obstruction and Infection. Large urinary tract stone may block the urinary tract and lead to infection. This is because waste products are unable to pass the blockage, which may cause a build-up of bacteria.
• Chronic Kidney Disease. People with urinary tract stones face a higher risk for chronic kidney disease, particularly if they also have diabetes, high blood pressure, or frequent urinary tract infections. Having chronic kidney disease, in turn, can increase the risk for cardiovascular diseases, which is further could be aggravated by urinary tract stones;
• Kidney Failure. It is very rare for urinary tract stones to cause kidney failure. However, some people have risk factors that make them more vulnerable to this serious complication, such as: Very frequent stone recurrences, episodes of urinary tract infections with obstruction, and a history of undergoing many procedures for urinary tract stones;
• Treatment complications. The different kinds of treatment for larger stones may cause some health problems. Possible complications will depend on which treatment the patient have, and the size and position of the stones. They could include:
  • Sepsis (widespread inflammation);
  • Ureter injury;
  • Urinary tract infection (UTI);
  • Bleeding;
  • Pain.

• Sufficient water intake. Having as much as 1.9 to 2.8 liters of water a day will help dilute minerals and flush out the urinary system day by day, thus reduce the chance of crystallization;
• Treating Underlying Conditions Known to Cause Urinary tract stones. Such disorders include distal renal tubular acidosis, hyperparathyroidism, sarcoidosis, and certain cancers;
• Dietary Considerations. People with urinary tract stones appear to be more sensitive to certain foods than people who do not form urinary tract stones. Therefore, vulnerable people should make specific changes in their diet. They should work with their doctors to develop a dietary plan that fits their individual situation. From these dietary guidelines:
  • Oxalate-restriction. If the person tends to form calcium oxalate stones, he is advised to limit consumption of oxalate rich foods, such as rhubarb, beets, okra, spinach, Swiss chard, sweet potatoes, nuts, tea, chocolate and soy products;
  • Salt Restriction. Sodium may increase levels of "urate", the crystalline substance that can trigger the formation of recurrent calcium oxalate stones. Patients with calcium stones should limit their sodium intake to 1,500 mg or less a day;
  • Protein Restriction. Protein increases uric acid, calcium, and oxalate levels in the urine. Restriction should particularly focus of meat and other animal derivatives;
  • Purine restriction for People who are at risk for uric acid stones. A high intake of purines can increase the amount of uric acid in the urine. Restricted food includes: Organ meats, alcohol, anchovies, sardines, oils, herring, mushrooms, spinach and cauliflower;
• Medication that can control the amount of minerals and acid in the urine and may help people who are at risk for certain kinds of stones, as the following:
  • Calcium stones (thiazide diuretic, phosphate-containing preparation);
  • Uric acid stones (allopurinol);
  • Struvite stones (Long-term use of antibiotics in small doses);
  • Cystine stones (Mercaptopropionyl glycine, potassium citrate).

Between 80-85% of crystals remain tiny enough to travel through the urinary tract and leave the body in the urine without being noticed. Larger stones are able to be eliminated throw seeking medical care with many procedures. Without treatment, calcium stones recur in 50% of patients within 5 years of the first attack, and in 70% of patients or more within 10 years. The individual risk for recurrence varies depending on the stone kind and the underlying condition.

Medical therapy is generally effective at delaying (but perhaps not completely stopping) the tendency for stone formation. Metabolic evaluation and treatment are indicated for patients at greater risk for recurrence, including those who present with multiple stones, who have a personal or family history of previous stone formation, who present with stones at a younger age, or who have residual stones after treatment.

Anyone can get a urinary tract stone, but some people are more likely to get one. Men are affected more often than women, and Caucasians are more prone to urinary tract stones than African Americans. Age is also a factor. The chance of getting a urinary tract stone rises as men enter their 40s and continues to rise into their 70s. For women, the risk peaks in their 50s.

Experts say that the incidence of urinary tract stones is on the rise. According to the National Health and Nutrition Examination Survey, as of 2012, 10.6% of men and 7.1% of women in the United States are affected by renal stone disease, compared to just 6.3% of men and 4.1% of women that were affected in 1994. Changing socio-economic conditions and subsequent lifestyle may be linked to changes in the prevalence, incidence and distribution for age, sex and type of urolithiasis in terms of both the site and the chemical-physical composition of the calculi.