Kidney Stones Diagnosis

  • Diagnosis

    Kidney stones are abnormal, hard, chemical deposits that form inside your kidneys. Kidney stones are a common problem, with about 10% of Americans expected to pass at least one kidney stone in their lifetime. Stones come in various shapes, colors, and sizes; they can be as small as a grain of sand, the size of peas or marbles, or even as large as your fist.

    Kidney stones are not related to gallstones. The two types of stones occur in different parts of the body, and having one does not affect your risk of developing the other.

    The kidneys are two bean-shaped organs about the size of an adult’s fist, located below the ribs and toward your back. They filter and clean the blood and manufacture urine Figure 01.

    Click to enlarge: Anatomy of the kidneys

    Figure 01. Anatomy of the kidneys

    Some of the substances that are filtered by the kidneys tend to form crystals, while others help prevent crystal formation. Normally the kidneys can maintain a balance, but if the system becomes disrupted, the balance may tip toward crystal formation. Crystals will begin to stick together and, over a period of months or years, will form a stone. Substances that can form crystals include calcium, oxalate (oxalic acid), uric acid, and cystine. Those that prevent crystal formation include citrate and magnesium. Most kidney stones consist primarily of calcium.

    While small stones often pass out of the body in the urine without causing any pain or discomfort, larger stones can become trapped in your urinary tract and may cause extreme pain, blocked urine flow, urinary infections, or blood in the urine.

    Kidney stones may be found in the kidney, the tube that drains the urine from the kidney to the bladder (the ureter), or the bladder. Urinary stones may develop inside the kidneys when minerals and other substances in the urine form crystals that build up over time to form a small, stone-like mass. Stones may stay in the kidney or break loose and travel down the ureter toward the bladder.

    A stone that remains in your kidney usually doesn’t cause any problems unless it becomes so large that it blocks the flow of urine or becomes infected. Small stones that become trapped in the ureter can cause urinary tract infection, obstruction of urinary flow or kidney damage. If a large stone becomes stuck in the narrow ureter, it can cause severe pain.

    Most stones will pass from the body spontaneously, but several treatment options are available for those that will not pass. Treatment measures, as well as measures to prevent the formation of new stones, depend on the size, location, and type of kidney stone you have. Your family physician may treat this condition or refer you to a urologist, a physician who specializes in the surgical treatment of urinary diseases, or to a nephrologist, who specializes in the medical management of kidney diseases.

    The formation of kidney stones is complex, but there are at least two mechanisms that play a role in their development: excess amounts of the substances in the urine that may promote crystal formation and the physical and chemical changes that cause the crystals to turn into stones.

    These changes may be caused by diet, drugs, heredity, climate, or other medical conditions. In a small number of cases, the cause of kidney stones cannot be determined.

    While certain foods that are high in protein, such as meat, may encourage formation of kidney stones, this mainly occurs in people who are susceptible to this condition. If you are not prone to kidney stones because of genetic factors, medical conditions, or other reasons, it is unlikely that eating any specific food will cause you to develop kidney stones.

    There are four major types of kidney stones, and each has a different cause. Stones are classified according to their chemical composition.

    Approximately 75% to 85% of all kidney stones are calcium stones. These stones are made up of calcium and oxalate or calcium and phosphate and may result from having too much of either of those substances in your urine. High calcium concentrations can result from ingestion of large quantities of vitamin C, excess animal protein or excess salt. Not enough dietary calcium or potassium can increase the risk of calcium stones. Low urine volume and low fluid intake along with such medical problems as gout, diabetes, obesity and the other endocrine problems can increase the risk of calcium stones.

    Struvite stones usually result from urinary infections caused by a particular bacterium and are found mainly in women. They account for 10% to 15% of all cases of kidney stones. Struvite stones can also develop in patients who have long-term bladder catheters.

    Uric acid stones are caused by having high levels of uric acid in your urine, which may happen if you eat a lot of meat, if you have gout, or if you are receiving chemotherapy. In addition, uric acid stones may form if the acid level in the urine is high. Uric acid is a byproduct of protein metabolism. Uric acid stones are much less common than calcium stones, accounting for only 5% to 10% of all kidney stones.

    Cystine stones are the rarest type of kidney stones, affecting 1% to 3% of patients. They are made up of cystine, an amino acid. The buildup of cystine in the urine that leads to cystine stones is caused by a rare genetic disorder.

    Pain is the most typical symptom associated with kidney stones. Passing a kidney stone can be one of the most painful experiences you may ever go through. However, kidney stones may develop without causing any pain, or cause only mild pain Table 01. While small stones are more likely to pass from the body without causing any discomfort, size does not always predict the severity of pain. A small stone that causes acute obstruction of the urinary tract can cause more pain than a large stone that is not associated with obstruction.

    Table 1.  Symptoms of Kidney Stones

    Severe pain in your back or side, with or without nausea or vomiting.
    Burning and discomfort during urination.
    Blood in the urine.
    A persistent urge to urinate or unusually frequent urination.

    When a stone becomes trapped in the narrow ureter, it may cause severe pain in the back or side. You may experience nausea and vomiting as well. There may be blood in the urine, although sometimes in such tiny amounts that it would be visible only through a microscopic examination.

    Pain usually begins abruptly on one side of your body, then becomes constant and intense. If the pain is in the flank area, to the side of the back near the waist, it means that the stone is probably in the kidney or upper urinary tract. If the pain shifts downward, toward the groin, the stone is traveling downward through the ureter closer to the bladder. Blood may appear in your urine as the stone grows or tries to squeeze through the narrow ureter. As the stone approaches the bladder, you may feel an increased urge to urinate or experience a burning sensation during urination. You may develop fever and chills, possible signs of an infection.

    A number of factors may increase your risk of developing kidney stones. They include family and personal history, age, gender, race, certain diseases and medications, diet, fluid intake, and activity level.

    If a member of your family has kidney stones, you are more likely to develop them too. If you have already had one or more kidney stones, you also have an increased risk of recurrence.

    Kidney stones are most likely to occur in people between the ages of 30 and 50. Kidney stones are rare in children unless they are caused by certain inherited disorders.

    Men are more likely than women to develop kidney stones, although the incidence in women has been increasing in recent years.

    The incidence of kidney stones is higher in Caucasians than in African-Americans.

    Common medical conditions such as chronic urinary tract infections, gout, cystic kidney disease, and hyperparathyroidism can increase your risk of developing kidney stones.

    Lack of fluid intake can affect your risk of developing kidney stones, particularly if you are prone to this condition. If you are susceptible to kidney stones and become dehydrated, your urine will contain a higher concentration of the chemicals that can form crystals and, ultimately, stones. If you live in a warm climate or work outdoors in hot weather, you may have a higher risk of developing kidney stones unless you drink plenty of fluids, especially water.

    A diet high in protein, from sources such as meat, chicken, or fish, may increase your risk, as could a diet low in fiber from sources such as fruit and vegetables.

    Your risk of developing kidney stones may increase if you lead a sedentary lifestyle. If you are paralyzed or are bedridden for a lengthy period, your risk may increase because your lack of physical activity causes your bones to release more calcium.

    Most kidney stones are discovered when patients go to their doctors with complaints of back or kidney pain, blood in the urine, or chronic urinary infections. If your doctor suspects kidney stones, he or she will ask you about your medical and family history and conduct a physical examination. The doctor will be particularly interested in aspects of your diet that may increase your risk of developing kidney stones, such as your fluid intake and consumption of calcium, animal protein, salt, and foods high in oxalate (including spinach, nuts, chocolate, and tea). You will also be asked whether you are taking any medications that may promote formation of kidney stones.

    The doctor will request a chemical analysis of your blood, a urine sample, or a 24-hour collection of urine to see whether you have an infection or have high levels of substances that form kidney stones.

    The doctor may order an x-ray or ultrasound to locate a stone that is stuck in your urinary system. These diagnostic techniques can also help the doctor estimate the size of the stone. The doctor may order a type of x-ray known as an intravenous pyelogram to look for stones that don’t show up on traditional x-rays. For this test, a special contrast dye is injected into a vein in your arm. A series of images are taken as the dye moves through your kidneys, ureters, and bladder, enabling doctors to locate the position of the stone and examine the condition of these organs. Alternatively, a non-contrast spiral CT (CAT scan) can be used to identify stones in the kidney or ureter without the use of contrast dye. During the test, you will be placed in the large CT scanner and a series of multiple images can be obtained in about 10 minutes.

    If you pass a kidney stone, it should be saved and given to your doctor for laboratory evaluation. Treatment and preventive measures are based on the type of stone you have. If you are about to pass a stone, you may be asked to urinate through a strainer so that the stone can be preserved and analyzed. You should save all the pieces of a stone, no matter how small. However, a 24-hour urine collection will ultimately be the best laboratory test to identify the underlying cause(s) of your stone disease.

    Prevention is extremely important if you have already had at least one kidney stone, since you are likely to form another. The most effective preventive measure against kidney stones is to drink more liquids, especially water. If you have had kidney stones, you should drink enough liquids to produce at least two and a half quarts of urine in every 24-hour period. This means that you need to drink about 10 to 12 ten-ounce glasses of fluid each day, and at least half of them should be water. If you live in a hot, dry climate, you may need to drink even more fluids. Spread your fluid intake as evenly as possible throughout the day to prevent your urine from becoming too concentrated.

    If you have passed a stone or had one removed, the doctor may suggest preventive steps based on the stone’s chemical composition and results of your 24-hour urine samples. These steps may include changes in your diet and perhaps medication(s). Your doctor may recommend dietary changes such as increasing your fiber, and lowering consumption of:

    • protein, found in meat, fish, and poultry
    • salt
    • oxalate, found in spinach, rhubarb, beets, strawberries, nuts

    It is very important that you check with your doctor before making any modifications to your diet. Not everyone needs to make changes, and cutting out food groups can be harmful. Also check with your doctor before taking any dietary supplements, vitamins, or minerals.

    If you are in extreme pain from what may be a kidney stone, contact your doctor or seek help at a hospital emergency room. The doctor will order imaging tests such as an intravenous pyelogram or a spiral CT to check for stones. Blood and urine tests will also be performed.

    An IVP is a special x-ray exam of your kidneys and other parts of your urinary system. This includes the tubes leading from the kidneys (ureters) and your bladder. A special dye is injected into your bloodstream through an IV so that the x-ray machine can pick up images of your kidneys and other parts of your urinary tract. The exam takes about an hour and should not be painful.

    A spiral CT exam is another special type of x-ray. The spiral CT scan is a painless procedure that involves a highly advanced imaging machine. The machine rotates rapidly around the body taking over one hundred pictures in sequence. The scan is so sensitive that it can spot stones that are too small to be seen on a conventional x-ray.

    You may be able to pass a stone through your urinary system without seeking medical treatment. Drink two to three quarts of water a day and stay physically active. You may take pain medication as needed. If you think you are about to pass a stone, urinate through a strainer or into a cup so that you can save the stone and give it to your doctor for testing.

    Your doctor is the best source of information on the drug treatment choices available to you.

    Surgical procedures are used to treat kidney stones that are too large to pass through the body on their own or are causing bleeding, kidney damage, or chronic urinary infections. The most commonly used procedure is shock wave lithotripsy (SWL), a process that breaks kidney stones into tiny fragments. Other procedures include percutaneous nephrolithotomy and ureteroscopic stone removal. Both of these procedures use miniature telescopes to look inside the kidney or ureter to remove stones.

    SWL relies on shock waves to break kidney stones into fragments or crystals that can pass out of the body in the urine. It is most effective on stones located in the kidney or upper urinary tract that are no larger than about three-quarters of an inch or one centimeter across. A machine called a lithotripter is used to focus shock waves from outside the body onto the stone.

    During SWL, you will be positioned in a water bath or asked to lie on a soft cushion while the shock waves are administered. You may be given a sedative just before the procedure to help you relax. Depending on patient and physician preferences, you may be given anesthesia instead. You will not feel the shock waves or experience pain from them; however, you will be given earphones to protect your ears from the noise they generate. Because several hundred shock waves will be needed to break up the stone, the procedure may last from half an hour to about two hours.

    The success rate of SWL is 60% to 90%, depending on the location of the stone. Complications may include bruising on the back or abdomen, blood in the urine, and discomfort as the shattered fragments of the stone move through your urinary tract. You should be able to resume a normal schedule within a few days.

    If an SWL procedure does not completely break up the kidney stone, you may need to undergo additional treatments. Your doctor also may perform ureteroscopic stone removal. In this procedure, a surgeon will insert a small telescope called a uretoscope into the ureter. The stone is then grasped with forceps and removed. A large stone may be shattered first with one of several different techniques. In addition to being used as a follow-up procedure to SWL, ureteroscopic stone removal is often used as a primary treatment to remove stones lodged in the ureter.

    Percutaneous nephrolithotomy is used when SWL is not effective or the stone is exceptionally large or inaccessible. In this procedure, the surgeon makes a tiny incision in your back, then inserts a larger telescope called a nephroscope. The stone is then located and removed. Large stones are generally broken into smaller pieces before removal.

    The prognosis depends on the cause of your kidney stone and your willingness to take medication, if prescribed, or follow other steps your doctor has recommended, such as diet and lifestyle changes. If you do not adhere to treatment recommendations, you may develop a new stone every two to three years. However, if you follow the prescribed recommendations, the medications and/or dietary changes can reduce your chance of forming another stone by 90% to 95%.

    If you have had treatment for a kidney stone, such as SWL, but continue to experience pain, contact your physician. Some pieces of the stone may still be stuck in your urinary tract and will require additional treatment. Otherwise, follow the doctor’s recommendations for prevention of additional stones and routine check-ups.

  • Prevention and Screening

    Prevention is extremely important if you have already had at least one kidney stone, since you are likely to form another. The most effective preventive measure against kidney stones is to drink more liquids, especially water. If you have had kidney stones, you should drink enough liquids to produce at least two and a half quarts of urine in every 24-hour period. This means that you need to drink about 10 to 12 ten-ounce glasses of fluid each day, and at least half of them should be water. If you live in a hot, dry climate, you may need to drink even more fluids. Spread your fluid intake as evenly as possible throughout the day to prevent your urine from becoming too concentrated.

    If you have passed a stone or had one removed, the doctor may suggest preventive steps based on the stone’s chemical composition and results of your 24-hour urine samples. These steps may include changes in your diet and perhaps medication(s). Your doctor may recommend dietary changes such as increasing your fiber, and lowering consumption of:

    • protein, found in meat, fish, and poultry
    • salt
    • oxalate, found in spinach, rhubarb, beets, strawberries, nuts

    It is very important that you check with your doctor before making any modifications to your diet. Not everyone needs to make changes, and cutting out food groups can be harmful. Also check with your doctor before taking any dietary supplements, vitamins, or minerals.

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