Kidney stones are solid accumulations of material that form through precipitation in the tubal system of the kidney. Kidney stones cause problems when they block the flow of urine through or out of the kidney. When the stones move along the ureter, they cause severe pain.
Gallbladder stones are solid accumulations of material that form through precipitation in the liver and then move into the gall bladder. They cause problems when they block the flow of bile out of the liver or out of the gall bladder. They can cause attacks of gall bladder disease (cholecystitis), hepatitis, or pancreatitis. They can also cause severe pain.
The purpose of analyzing kidney and gallbladder stones is to determine the source of the stones. Different materials can form stones. Once the source of the stones is known, steps can be taken to prevent subsequent formation.
An adequately stocked laboratory is needed for accurate analysis of stones. The most difficult aspect of stone analysis is obtaining the stones.
Passing a kidney stone is exquisitely painful. Once passed, persons with stones must strain their urine to recover any stones. Retrieving a kidney stone is painful for the person experiencing the stone. It also requires skill on the part of an operator to retrieve the stone.
A gallbladder stone must also be obtained before chemical analysis can be performed. Gallbladder stones can become lodged at several locations and cause considerable pain and discomfort. Retrieving a stone usually requires surgery. Commonly, the gallbladder is removed in the process of collecting a stone.
Urine is formed by the kidneys. The kidney is made up of microscopic units called nephrons. Each nephron contains a capillary tuft (glomerulus) and a tubule. Blood flows into the kidneys, and engorges the capillary tufts. Water and small solutes pass through the vessel walls forming a filtrate of the plasma that enters the underlying space (Bowman's capsule). The walls of the capsule form a tubule that traverses the kidney. The cells of the tubule modify the filtrate along its length ultimately forming the urine, which passes out of the body. Sometimes, a problem causes the dissolved solutes to become supersaturated resulting in the formation of crystals. When tiny crystals associate together they form a larger solid mass called a kidney stone or calculus. A kidney stone is also called a nephrolith or urolith (nephro- refers to the kidney, uro- refers to urine, and -lith means stone). Kidney stones have multifactorial causes, but some predisposing conditions are:
- Diet: Excessive calcium in water and foods rich in oxalate or purines can lead to excessive excretion of calcium, oxalate, and uric acid in urine. Dehydration: Water deprivation or loss from other sources causes stasis in the tubules and concentrates the solutes there.
- Deficiency of inhibitors: Some dietary substances such as ascorbic acid and citric acid promote loss of organic calcium salts that are soluble. Absence of these can lead to excessive amounts of oxalate and phosphate.
- Drugs: Some drugs such as tetracycline are poorly soluble and may precipitate, forming stones or becoming part of the stone matrix.
- Metabolic disorders: Hyperparathyroidism causes excessive calcium excretion by the kidneys. Cystine stones form because of a defect in the renal tubular reabsorption of dibasic amino acids, a condition known as cystinuria.
- Genetics: Some people produce and excrete greater quantities of certain metabolites such as uric acid.
- pH: Most solutes are only soluble within a finite pH range. For example, phosphates and carbonates are insoluble at an alkaline pH. Uric acid and calcium oxalate are insoluble at an acidic pH. People who produce chronic acid urine are more prone to develop uric acid and calcium oxalate crystals.
Many people never find out that they have stones in their kidneys. These stones are small enough to allow the kidney to continue functioning normally, never causing any pain. These are called "silent stones." Kidney stones cause problems when they interfere with the normal flow of urine. They can block (obstruct) the flow down the tube (the ureter) that carries urine from the kidney to the bladder. The kidney does not normally experience any back pressure. When pressure builds from backed-up urine, the kidney may swell (hydronephrosis). If the kidney is subjected to this pressure for some time, it may cause damage to the delicate kidney structures. In the most severe case, this back pressure causes the pressure in Bowman's space to equal the blood pressure in the glomerular capillaries and filtration stops. The person stops producing urine, and waste products accumulate in the blood leading to renal failure. When the kidney stone is lodged further down the ureter, the backed-up urine may also cause the ureter to swell (hydroureter). Because the ureters are muscular tubes, the presence of a stone will make these muscular tubes spasm, causing severe pain.
About 10% of all people will have a kidney stone in their lifetimes. Kidney stones are most common among:
- people over the age of 30
- people who previously have had kidney stones
- relatives of persons with kidney stones
Approximately 80% of gallbladder stones are primarily cholesterol (over 70% cholesterol by weight). They also contain bile pigments, bile acids, fatty acids, and calcium salts. The remainder of gall stones are primarily made of bilirubin. The primary constituents are calcium bilirubinate, calcium phosphate, and calcium carbonate. A gallbladder stone is also called a cholelith (chole- refers to the gallbladder and -lith means stone). Cholesterol-rich gallbladder stones typically develop when the following three conditions exist:
- supersaturation of gallbladder, due mainly to increased biliary cholesterol secretion
- abnormally rapid precipitation of micro-crystals of cholesterol due to an excess of promoters and/or a shortage of inhibitors of crystallization
- stasis within the gallbladder due to the combination of impaired motility, primarily reduced emptying in response to food and/or crystal trapping by an abnormally thick mucous glycoprotein on the gallbladder lining
Many people do not realize that they have stones in their gallbladders. These stones are small enough to allow the liver, gallbladder, and pancreas to continue functioning normally, never causing any pain. Gallbladder stones cause problems when they interfere with the normal flow of bile. They can obstruct the flow down the common bile duct that carries bile from the gallbladder to the small intestine. Gall stones may obstruct the pancreatic duct, the tube that connects the pancreas with the common bile duct. This can cause inflammation of the pancreas (pancreatitis). The pancreas and gallbladder do not normally experience any back pressure. When pressure builds from backed-up bile (gall bladder) or pancreatic secretions (pancreas), swelling will occur. If the pancreas is subjected to this pressure for some time, it may cause damage to the internal structures of the organ. When the gallbladder is subjected to pressure, it simply enlarges and exerts pressure on the liver. When a gallbladder stone is lodged at the end of the common bile duct (in the Sphincter of Oddi where it opens into the small intestine), the backed-up bile may also cause all of the structures (liver, gall bladder, pancreas, and ducts) to swell. Because the ducts have muscle tissue in their walls, the presence of a stone will make them spasm, causing pain.
About 12% of men and 25% of all women will develop gallstones in their lifetimes. Gallbladder stones are most common among:
- women who have had children
- people over the age of 40
- people who previously have had gallbladder stones
- people who are overweight
Composition of stones
Kidney stones can be composed of a variety of substances. About three-fourths of kidney stones contain calcium. The most prevalent kidney stone is made up of calcium oxalate usually in combination with other calcium salts. In addition to the chemical name, stones are often described by their mineralogical properties. For example, calcium oxalate exists in two forms, the monohydrate which is called whewellite and the dihydrate which is called weddellite. The most common types of kidney stones include:
- calcium oxalate (whewellite and weddellite)
- magnesium ammonium phosphate (struvite)
- tricalcium phosphate (whitlockite); calcium phosphate (apatite); and calcium hydrogen phosphate dihydrate (brushite)
- uric acid stones
Gallbladder stones are usually composed of cholesterol. They also contain some:
- bile pigments
- bile acid
- calcium salts
People who have kidney stones usually do not have symptoms until the stones pass into the ureter. Prior to this, some individuals may notice blood in their urine. Once the stone is in the ureter, however, most people will experience bouts of very severe pain. The pain is crampy and spasmodic, and is referred to as "colic." The pain usually begins in the flank region, the area between the lower ribs and the pelvis. As the stone moves closer to the bladder, a person will often feel the pain radiating along the inner thigh. In women, the pain may be felt in the vulva. In men, the pain may be felt in the testicles. Nausea, vomiting, extremely frequent and painful urination, and obvious blood in the urine are common. Fever and chills usually mean that the ureter has become obstructed, allowing bacteria to become trapped in the kidney causing a kidney infection (pyelonephritis).
People who have gallbladder stones usually do not have symptoms until the stones pass into the common bile duct. Once the stone is in the common bile duct, however, most people will experience bouts of pain, especially after eating fatty meals. The pain is also referred to as colicky. The pain usually begins in the upper right quadrant of the abdomen, the area just beneath the right ribs. As the stone moves closer to the Sphincter of Oddi, a person will often feel the pain radiating throughout the entire abdomen. If it obstructs the pancreatic duct, it may be felt in the posterior portion of the abdomen as flank pain. Nausea, vomiting, light (clay) colored stools, and flatulence are common. Fever and chills usually mean that the Sphincter of Oddi has become obstructed, forcing pancreatic fluid and liver discharges to be trapped in their respective organs, often causing inflammation of the liver (hepatitis), gallbladder (cholecystitis), and pancreas (pancreatitis).
Kidney stones that are less than 5 mm in diameter are usually passed. The physician or nurse must instruct the patient in the proper technique to recover the stone once it is passed. Special laboratory equipment is required for stone analysis. Most clinical laboratories do not perform this service. Consequently the stone must be packaged and mailed to a reference laboratory that performs stone analysis.
For the most part, the analysis is qualitative in nature. Testing involves macroscopic evaluation of the stone. This includes determination of its weight, size, shape, hardness, and color. Kidney stones are usually analyzed by x ray diffraction. The stone is pulverized into a fine powder and the powder is spread over a glass fiber mat and exposed to x rays. The crystals scatter the x rays and the various patterns produced are analyzed to determine the chemical composition. The composition of noncrystalline stones cannot be determined by this method and are usually analyzed by infrared spectroscopy. These crystals are usually composed of drugs or their metabolites that precipitated in the tubules. In special cases the stone may be analyzed by chemical analysis and by microscopic analysis. For example, cystine stones can be readily detected by grinding a small piece of the stone into a powder. The powder is boiled in a small amount of deionized water and a solution of sodium cyanide is added. The cyanide reduces the cystine to cystiene. After standing for five minutes, several drops of sodium nitroprusside are added. The solution will turn red if cystiene is present. Gall stones are composed of either cholesterol or bilirubin. These can be analyzed by infrared analysis, x-ray diffraction or chemical analysis (detection of cholesterol and bilirubin after organic extracton).
Many stones can be seen using a basic x ray, but some cannot. A more sensitive imaging procedure is to use a series of x rays taken after injecting iodine dye into a vein. This procedure is called an intravenous pyelogram (IVP). The dye allows the urinary system to be visualized. In the case of an obstruction, the dye will be stopped by the stone or will only be able to get past the stone at a slow trickle.
A cholangiogram is used to visualize the location of a gallbladder stone that is causing an obstruction. A tube is passed through the mouth, throat, and stomach. It enters the small intestine and is inserted into the Sphincter of Oddi. Dye is injected, allowing the interior of the common bile duct and connected structures to be visualized. As with a kidney stone, the dye is stopped by an obstruction, allowing a radiographer to pinpoint the position of a stone. A CT or MRI scan may also be used to locate a gallbladder stone.
Persons are prepared prior to obtaining a stone for analysis. Preparation for surgery (gallstones) involves anesthesia. Preparation for collecting passed kidney stones involves straining urine through a special sieve. Preparation for surgical collection of a kidney stone involves sedation and passing a catheter through a person's urethra and bladder before entering the ureter.
After stones have been analyzed, the goal becomes preventing subsequent formation by eliminating the cause of the stone.
Prevention of kidney stones depends on the type of stone and the presence of an underlying disease. In almost all cases, increasing fluid intake so that a person consistently drinks several quarts of water a day is an important preventive measure. Persons with calcium stones may benefit from taking a medication called a diuretic, which has the effect of decreasing the amount of calcium passed in the urine. Eating less meat, fish, and chicken may be helpful for individuals with calcium oxalate stones. Other items in the diet that may encourage calcium oxalate stone formation include beer, black pepper, berries, broccoli, chocolate, spinach, and tea. Uric acid stones may require treatment with a medication called allopurinol. Struvite stones will require removal and an affected person should receive an antibiotic. Adjustment of pH is an important preventive measure. For example, if the stone contains calcium phosphate or calcium carbonate or a mixture of these, an acidifier is used to keep the urine pH below seven because these stones form in alkaline urine. When a disease is identified as the cause of stone formation, treatment specific to that disease may lessen the likelihood of repeated stones.
Preventing gallbladder stones is usually accomplished by dietary modification. Fat intake must be diminished. This will also prevent intestinal colic as the gallbladder is usually removed. Drugs that inhibit the formation of cholesterol by the liver may be used. Niacin, cholestyramine, cholestipol, lovastatin, simvastatin, pravastatin, fluvaststin, and gemfibrazol have all been approved for use in the United States as of 2001. Some experts recommend daily supplements of methionine. The drug ursodiol (Actigall) has also been approved for treatment of gallbladder stones.
Complications of actual stone analysis include laboratory error. These are very rare.
Complications for people with stones include recurrence. They also may include adverse drug reactions. These, too, are uncommon.
A person with a kidney stone will say that the most important aspect of treatment is adequate pain relief. Because the pain of passing a kidney stone is so severe, narcotic pain medications (such as meperidine or morphine) are often required. It is believed that stones may pass more quickly if a person is encouraged to drink large amounts of water (2-3 quarts, or 2-3 L per day). If an individual is vomiting or unable to drink because of the pain, it may be necessary to provide fluids through a vein. If symptoms and urine tests indicate the presence of infection, antibiotics will be required.
A person with a gallbladder stone also finds that the most important aspect of treatment is adequate pain relief. Because the pain of gallbladder disease attacks are so uncomfortable, pain medications (such as ibuprofen or acetaminophen with codeine) are often required. If symptoms and tests indicate the presence of infection, antibiotics will be required.
Although most kidney stones will pass on their own, some will not. Surgical removal of a stone may become necessary when a stone appears too large to pass. Surgery may also be required if the stone is causing serious obstructions, pain that cannot be treated, heavy bleeding, or infection. Several alternatives exist for removing stones. One method involves passing a tube into the bladder and up into the ureter. A tiny basket is then passed through the tube, and an attempt is made to snare the stone and pull it out. Open surgery to remove an obstructing kidney stone was relatively common in the past, but current methods allow the stone to be crushed with shock waves (called lithotripsy ). These shock waves may be aimed at the stone from outside of the body by passing the necessary equipment through the bladder and into the ureter. The shock waves may be aimed at the stone from inside the body by placing the instrument through a tiny incision located near the stone. The stone fragments may then pass on their own or may be removed through the incision. All of these methods reduce an individual's recovery time considerably when compared to the traditional open operation.
An individual with a gallbladder stone will usually have the gallbladder removed. The most common procedure for this task is a laparoscopic cholecystectomy. Three small incisions are made in the abdomen. Into one, a thin tube with a light and camera lens is passed. Into the second and third, thin tubes through which instruments are inserted, are passed. A surgeon visualizes the interior of the abdomen on a television screen using the camera in the first tube and removes the gall bladder using the instruments inserted through the second and third tubes. Using this approach, postsurgical complications have been reduced, and the time required for recovery has been significantly reduced (when compared to traditional open surgical techniques).
Health care team roles
A physician makes an initial diagnosis of kidney or gall stones. A radiologist confirms the diagnosis using x rays or ultrasonography. A surgeon is needed to operatively remove a kidney or gall stone. Lithotripsy is performed by a technician under the supervision of a physician. Occasionally, open surgery is required and is performed by a surgeon. Nurses assist in lithotripsy and surgery. A laboratory specialist performs a chemical analysis of the stone to determine its composition and origin. Pharmacists may dispense pain medications and antibiotics as required.
Cholangiogram— X-ray technique used to visualize gallbladder stones.
Cholecystitis— Inflammation of the gallbladder.
Cholelith— Gallbladder stone.
Hepatitis— Inflammation of the liver.
Hydronephrosis— Swelling of a kidney due to elevated pressure from excess fluid accumulation.
Hydroureter— Swelling of a ureter due to elevated pressure from excess fluid accumulation.
Intravenous pyelogram (IVP)— X-ray technique used to visualize kidney stones.
Laparoscopic cholecystectomy— Surgical procedure for removing a gallbladder.
Lithotripsy— Technique that uses focused sound waves to pulverize kidney stones, thus avoiding surgery.
Nephrolith— Kidney stone.
Nephron— Tube within the kidney that processes filtrate from the blood, reclaiming some substances and creating urine.
Pancreatitis— Inflammation of the pancreas.
Pyelonephritis— Infection of the kidney.
Sphincter of Oddi— The opening of the common bile duct into the small intestine.
Ureter— Tube that connects the kidney and urinary bladder. Its function is to transport urine.
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