Kidney Stones

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Evaluation for kidney stones may be performed in a variety of settings depending upon an individual's circumstances. For people without symptoms whose kidney stones were found incidentally, for example in an MRI being performed for another reason, their testing may be scheduled ahead of time to occur in a doctor's office. For others, the symptoms may lead them to seek immediate medical attention in the emergency department of a hospital or an urgent care center where their exam, testing, and diagnosis will occur. The circumstances under which testing occurs may dictate the tests performed, but for all evaluations, the goal is to determine the size, shape, and location of the kidney stone and assess the risk of infection.

Diagnosing kidney stones usually involves one or more imaging procedures to visualize the urinary tract and kidney stone and is usually accompanied by simple blood and urine tests to evaluate the function of the kidneys and rule out other conditions that may be causing your symptoms. A CT scan is the best imaging technique for evaluating kidney stones, but some medical centers may use ultrasound or a specialized abdominal X-ray technique known as intravenous pyelography.

Each evaluation begins with the medical history and physical exam, during which the doctor will collect information on any other signs and symptoms you may be experiencing and assess the characteristics of the pain, if any. During the visit, be prepared to discuss your and your family's medical history of kidney stones; your symptoms, including when they first appeared, how long they last, and the circumstances in which the symptoms occur; and any questions you have about your condition. During the physical exam, your doctor may palpate your abdomen and flanks, examine your groin and genital region, take your pulse at different locations on your body, and listen to the sounds of your heart and lungs.

Once this information has been obtained, follow-up testing will be recommended and may include any of the following:

  • Blood tests
  • Abdominal X-ray (Intravenous Pyelography)
  • Abdominal Ultrasound
  • CT scan
  • Urine test
  • Blood Tests

    Blood testing is performed for kidney stone evaluations. Samples of blood are collected and used to evaluate the basic function and condition of the kidneys and to rule out the possibility that other diseases are causing the symptoms.

    Preparing for a blood test usually requires abstaining from food and all beverages, with the exception of water, for nine to 12 hours prior to the blood draw. Check with your healthcare provider for detailed instructions. During the procedure, blood samples are drawn from a vein, usually from the inside of the elbow or the back of the hand, using a thin, hollow needle.

    Blood tests performed to diagnose and treat kidney stones include complete blood count (CBC) and creatinine levels. The CBC is a screening test used to diagnose many different diseases including those affecting fluid volume, anemia, blood loss, acute or chronic infection, allergies, and problems with clotting. The CBC includes evaluating the number of red and white blood cells, the total amount of hemoglobin, the fraction of blood consisting of red blood cells, and the size of the red blood cells, also known as mean corpuscular volume (MCV). For people who are scheduled to undergo an imaging technique that involves a contrast medium (material injected into the body to help distinguish internal structures), blood samples will be analyzed for creatinine levels to ensure that the kidneys are functioning normally and capable of filtering the contrast medium into the urine. If removal of the kidney stones involves a surgical procedure, the patient may need additional blood testing, depending on their medical condition.

    Abdominal X-ray (Intravenous Pyelography)

    In an X-ray, electromagnetic energy is used to create images of the internal organs and bones. X-rays rely on the differences in the density of materials; dense materials such as bones absorb more radiation than the soft tissue of the organs and muscles. Consequently, X-rays are very good at imaging bones, which are white on film, but are of limited value when imaging organs and tissues of the urinary tract (kidneys, ureter, bladder, and urethra), which are an undistinguishable shade of gray on X-rays. Furthermore, not all kidney stones show up on X-ray; uric acid stones and small kidney stones will not be revealed by a standard X-ray. Although X-rays are still sometimes used to evaluate kidney stones, they are largely being replaced by CT scans, which are a more accurate technique for imaging the urinary track and evaluating kidney stones.

    Intravenous pyelography is an X-ray exam that uses a contrast medium, which functions like a dye, to help visualize the urinary tract and detect the presence of a kidney stone. You should discuss with your doctor the use of contrast medium, usually iodine, and any potential for allergic reaction as well any preparations needed for the exam, such as dietary restrictions.

    An IVP begins with one or more plain X-rays of the abdomen. Then the contrast medium is injected into the arm, where it enters the bloodstream and travels to the kidneys. Additional X-rays are then taken while the dye moves through the urinary tract. During the procedure, a large bandage is used to apply pressure around the abdomen to improve the quality of the image obtained during an IVP. IVP studies are usually completed in about one hour but may require up to four hours from start to finish.

    Although X-rays themselves are painless, the use of the contrast medium with an IVP may cause some discomfort. The iodine may cause a slight sting as it is injected, and some patients experience a warm flush, a mild itching sensation, and a metallic taste in their mouth as the iodine circulates in the body. These sensations are usually short-lived and harmless. In rare instances, the contrast medium may cause shortness of breath or swelling in the throat. If any of these side effects occur, tell the radiologist or technician immediately.

    An IVP procedure exposes you to a small amount of radiation, roughly equivalent to typical background levels experienced over a six-month period. Women who have any chance of being pregnant should tell their doctors because the IVP procedure is usually not recommended for pregnant women.

    Abdominal Ultrasound

    Ultrasound uses the same sound-wave-based technology as prenatal sonograms and depth finders on boats. A small device that looks like a microphone, called a transducer or probe, directs ultrasound waves into the body. The sound waves, which are inaudible to the human ear, travel into the body and bounce back to a receiver, called an echocardiograph. The returning sound waves are analyzed by a computer to generate images that can be viewed on a video screen; in this case, the images depict the abdomen and urinary tract.

    Preparation for an ultrasound is straightforward and usually involves drinking four to six glasses of liquid about an hour before the test to fill your bladder and abstaining from food for eight to 12 hours before the test to avoid gas buildup in the intestines. Prior to the exam, you will be asked to remove all your clothing and jewelry and change into a gown. A technician applies a watery gel to the abdomen and then slides the transducer across the abdomen to scan the urinary tract. The procedure usually lasts about 15 to 30 minutes. Most patients say the procedure is painless, although some report slight discomfort from the pressure of the transducer on the abdomen.

    CT scan and CT Urogram

    Computed tomography is a noninvasive imaging technique that uses X-ray technology to depict internal structures of the body such as the urinary tract. All kidney stones are visible on CT scans. CT scans collect X-ray images from different angles around the body to generate detailed cross-sectional images as well as three-dimensional images of the body's internal structures and organs. A computer analyzes the radiation transmitted through the body to reconstruct the images of the internal structures and organs. The new generation of CT scans allows for faster, higher-quality imaging with less radiation exposure than a standard CT scan.

    Prior to the procedure you may be asked to abstain from eating or drinking. The procedure is painless and requires the patient to lie as still as possible on a table that is guided into a machine that resembles an enormous doughnut. The machine, called a gantry, directs small doses of electromagnetic radiation toward the body from various angles. Although an abdominal scan can usually be completed in a single breath, about 10 seconds or less, the entire procedure may last 5 to 30 minutes.

    A contrast medium (akin to a dye) is not necessary to diagnosis kidney stones with CT and typically is not used in emergency settings. However, if the examination is scheduled in a medical center, the urologist may follow a plain CT with a CT urogram, which uses a contrast medium to better visualize the structures of the urinary tract. If a contrast medium is to be used, patients typically will need to fast for a few hours before the procedure. The contrast medium will be injected into a vein during a CT scan. The contrast medium may, on occasion, cause an allergic reaction, most commonly hives or itchiness. In people with asthma, the allergic reaction may manifest as an asthma attack. In very rare instances, a patient may experience swelling in the throat or other areas of the body. If you experience hives, itchiness, or swelling in your throat during or after your CT scan, immediately tell the technologist or doctor.

    Abdominal CT scans involve exposure to a dose of radiation that is roughly equal to the background levels of radiation an average person experiences in three years. For most patients, the benefits far outweigh the risks associated with exposure to this level of radiation. However, pregnant women are usually advised to choose alternative testing procedures or postpone getting a CT scan until after they've delivered. People with pacemakers or internal cardioverter defibrillators who have been advised to avoid MRIs can safely have a CT scan.

    Urine Test

    Samples of urine are routinely collected for urinalysis as part of an exam for kidney stones. Standard urinalysis evaluates the urine for physical characteristics, chemical composition, and presence of substances such as bacteria that may indicate infection or blood. Blood in the urine is often not visible to the naked eye. Urine is also filtered to look for small kidney stones.

    Last reviewed on 10/13/09

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