Definition

A kidney stone is the result of a chemical reaction that occurs when the urine becomes concentrated and when certain substances combine together to create an object that is too large to pass in the urine. Calcium oxalate, calcium and ammonium phosphate, uric acid, cystine and other substances (such as calcium carbonate, magnesium, lysine, arginine and ornithine) in the urine crystallize to form a hard mineral deposit called a kidney stone.

Description

A kidney stone develops when substances in urine form crystals that stick together and grow in size. In most cases, these crystals are removed from the body by the flow of urine, but they sometimes stick to the lining of the kidney or settle in places where the urine flow fails to carry them away. These crystals may gather and grow into a stone, ranging in size from a grain of sand to a golf ball.

Most stones start in the kidney. Some may travel to other parts of the urinary system, such as the ureter (the tube leading from the kidney to the bladder) or bladder, and grow there. The most common types of kidney stones are calcium stones, uric acid stones, struvite stones and cystine stones.

Calcium stones are formed by a build-up of calcium, combining with oxalate, phosphate or carbonate. Calcium stones account for 75 to 85 percent of all stones and are more likely to occur in men.

Uric acid stones are formed by a build-up of uric acid. Uric acid stones account for 5 to 10 percent of all stones and are more likely to occur in men.

Struvite stones are formed by a build-up of calcium, magnesium and ammonium phosphate. Struvite stones account for 10 to 15 percent of all stones, are mainly found in women, and are linked to chronic infections of the urinary tract.

Cystine stones are formed by a build-up of cystine, combining with lysine, arginine and ornithine. Cystine stones account for 1 percent of all stones and are found in persons suffering from a hereditary disorder called cystinuria. Cystinuria occurs as a result of the kidney tubules not reabsorbing certain amino acids adequately. Cystine stones occurs in both men and women equally.

Causes and Risk Factors

The exact cause of kidney stones is unknown, however, there are a number of factors that may put a person "at risk" for kidney stones. The risk factors include:

• age - more common during middle age
• gender - three times more common in men than in women
• diet - eating a diet high in green vegetables, fat, diary products, salt and brewed tea
• a family history of kidney stones
• recurring urinary tract infections
• reduced water intake
• kidney disorders, such as cystic kidney diseases
• metabolic disturbances, such as bowel, endocrine and kidney problems
• genetic disorders, such as gout (a type of arthritis or inflammation about a joint caused by excess
• uric acid in the blood), cystinuria, primary hyperoxaluria and renal tubular acidosis (a condition in which the kidneys are unable to excrete normal amounts of acid)
• excess intake of vitamins C and D
• blockage of the urinary tract
• medications, such as diuretics (water pills) or calcium-based antacids
• bed confinement
• alcohol consumption

Symptoms

Kidney stones can form in some people without causing any symptoms, however, some stones may cause the following:

• severe pain, which usually starts suddenly and may last from minutes to hours, followed by long periods of relief. Kidney stone pain usually starts in the kidney or lower abdomen and later may move to the groin.
• nausea and vomiting
• burning and the urge to pass urine
• frequent urination
• cloudy or foul-smelling urine
• fever
• chills
• blood in the urine
• bloating
• pus in the urine

Diagnosis

The doctor will perform a number of diagnostic tests to diagnose kidney stones. Diagnostic tests include a blood test, a urine test and a 24-hour urine collection test. The 24-hour urine test is done to monitor urine volume, levels of acidity, and if a stone has passed into the sample, the make-up of stone (i.e., calcium-based, uric acid based, etc.) is also determined.

Other diagnostic tests include a kidney-ureter-bladder (KUB) x-ray, a kidney ultrasound, an intravenous pyelogram (IVP) and if recommended, a CAT (CT) scan.

A KUB x-ray involves low doses of electromagnetic energy to produce a picture of the kidney-ureter-bladder area. This x-ray will reveal kidney stones in these areas.

A kidney ultrasound is a diagnostic technique in which high frequency sound waves are passed into the kidney to detect obstructions and changes.

During an IVP, a colorless substance is injected into the vein. This substance circulates to the kidney and is excreted and concentrated, making the area in and around the kidney white. Obstructed and dilated areas will fill with white contrast much slower than normal.

A CT scan involves injecting a dye into the body that infiltrates the kidneys and accentuates the images. Using a series of cross-sectional x-rays, the images, made by the dye, make it possible to detect kidney stones.

Treatment

Fortunately, most stones can be treated without surgery. About 90 percent of all kidney stones can pass through the urinary system spontaneously with the help of plenty of water (two to three quarts a day) to help the stone move along. In addition to extra water consumption, the doctor may prescribe antibiotics to fight infection, pain relievers to help with the pain, an antispasmodic to relax the ureter muscles or diuretics to prevent urine from staying in the kidney. About 90 percent of all stones that leave the kidney will pass through the ureter within three to six weeks.

Surgical treatment is recommended if the stones:

• are too large to pass or have grown larger
• have not passed after a reasonable period of time
• are causing constant pain
• are blocking the urine flow
• cause ongoing urinary tract infections
• damage the kidney tissues

Surgical Treatment

Currently there are four (4) methods of stone removal:

Extracorporeal Shockwave Lithotripsy (ESWL)
ESWL uses non-electrical shock waves that are created outside of the body to travel through the skin and body tissues until the shockwaves hit the dense stones. The stones become sand-like and are passed. For this procedure, patients acre placed in a tub of warm, purified water or onto a water cushion machine that acts as a medium for transmitting these non-electrical shockwaves.

Percutaneous Nephrolithotomy (PNL)
Percutaneous nephrolithotomy is often used when the stone is quite large or in a location that does not allow effective use of extracorporeal shockwave lithotripsy (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 stone is located and removed. For large stones, an energy probe (ultrasonic or electrohydraulic) may be needed to break the stone into smaller pieces for removal.

Ureteroscopic Stone Removal
Ureteroscopic stone removal is achieved by passing a small fiberoptic instrument (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 or shatters it with a special instrument that produces a form of shockwave. A small tube (or stent) may be left in the ureter for several days after treatment to help the lining of the ureter to heal.

Open (incisional) Surgery
Open surgery involves opening the affected area and removing the stone(s). Another, less known procedure (called coagulum pyelolithotomy) also removes kidney stones. This procedure involves the injection of a liquid containing calcium chloride, cyroprecipitate, thrombin and indigo carmine into the kidney. This injection of substances forms a jelly-like clot that traps the stones inside. Through an incision made in the kidney, the doctor extracts the stone with forceps.

Prevention

People who have had more than one kidney stone are likely to form another. Therefore, prevention is very important. There are two types of preventive measures that help in preventing other kidney stones from developing: life-style changes and medical intervention.

Life-style changes include:

• Drink eight to 13 glasses of water (or at least two quarts) a day.
• Limit the amount of calcium and oxalate-based foods eaten. These include apples, black pepper, chocolate, coffee, cheese, grapes, ice cream, vitamin C, yogurt, tomatoes and oranges, to name a few.
• Limit the amount of animal protein eaten.
• Limit salt intake.
• Limit supplemental intake of vitamin C and D.
• Consult the doctor before taking vitamin supplements.
• Limit alcohol consumption.

Medical interventions include:

• For calcium stones, the doctor may prescribe thiazide diuretics or phosphate-containing preparations. Additionally, in hyperparathyroid patients, removal of all or part of the parathyroid glands located in the neck helps prevent further stone development.

• For uric stones, the doctor may prescribe allopurinol and a medicine to keep the urine alkaline.

• For struvite stones, the doctor will monitor the urine for bacteria on a regular basis. Additionally, if struvite stones cannot be removed, the doctor may prescribe acetohydroamic acid (AHA). AHA is used with long-term antibiotics to prevent the infection that leads to stone growth.

• For cystine stones, the doctor may prescribe Thiola. This medication helps reduce the amount of cystine in the urine.

Questions to Ask Your Doctor

• What tests need to be done to diagnose the condition or to locate the stones?
• Are there any risks to the tests?
• What type of stone has formed?
• What is the cause of the stones?
• What type of treatment are you recommending?
• How effective is the medication and treatment?
• Will you be recommending extracorporeal shockwave lithotripsy?
• What measures can be taken to prevent recurrence?
• Has any permanent damage occurred?