Urinary tract disorders often can be diagnosed through blood and urine tests. Blood tests can show when the kidneys are failing to adequately remove waste products. Urine tests (urinalysis) can show whether there is bleeding in the urinary tract, whether bacteria have infected the urinary tract, or whether the kidneys are functioning properly. A small sample of urine can be quickly tested for the presence of protein, sugar, blood, and other substances using a dipstick (a strip of paper coated with test chemicals that can be dipped into the urine and checked immediately for results). The relative amount of acid in the urine (pH) can be determined in the same way. Other urine tests require a person to collect all the urine he or she produces over a 24-hour period. Special imaging procedures also may be needed to examine the structure of the kidneys, ureters, bladder, and urethra. The following are the most common tests for diagnosing urinary tract disorders:
• Serum creatinine. This blood test measures the amount of creatinine, a waste product that results from eating meat and from muscle repair. High levels of creatinine in the blood indicate that the kidneys are not working properly.
• Blood urea nitrogen (BUN). Urea nitrogen is another by-product of protein digestion. As with serum creatinine, high BUN levels on a blood test indicate reduced kidney function.
Creatinine clearance. A creatinine clearance test compares the amount of creatinine present in a 24-hour urine sample with creatinine levels in blood to determine how much blood the kidneys have filtered over a 24-hour period. Specific gravity. This urine test measures the extent to which the kidneys can concentrate the urine they produce. If the specific gravity is lower than normal, it suggests that the kidneys are not functioning efficiently. Urinary sediment. Normal urine contains a small number of cells and other materials shed during passage through the urinary tract. Examining the number and type of these substances can help identify specific disorders. For example, the presence of white blood cells and bacteria indicates infection. The presence of white blood cells also may indicate a tumor. Crystals appear when the urine is not acidic enough to dissolve them or when the concentration of crystals in the urine is abnormally high. Casts (cylindrical clumps of material that form in and come from the tubules in the kidney) distinguish kidney problems from disorders of the ureter, bladder, and urethra and help identify the diseased area of the kidney.
Intravenous urography. This series of contrast medium-enhanced X rays allows doctors to view the interior structures of the urinary tract. This test sometimes is called an intravenous pyelogram, or IVP. The contrast medium is injected into a vein, and X rays are taken as it reaches the kidneys and is filtered out. When the contrast medium has filled your bladder, you will be asked to urinate, and X rays will be taken to see if any of the contrast medium remains in your bladder. This procedure is most often performed to look for stones in the kidney or the bladder, cysts in the kidney, tumors, an enlarged prostate, or other possible sources of blockage.
Cystoscopy. For this test, a thin, rigid or flexible tube (with or without a video camera attached) is passed through the urethra into the bladder. This procedure is required to rule out a possible bladder tumor.
Retrograde pyelogram. This procedure usually is performed during a cystoscopy and is used when poor kidney function limits the value of intravenous urography. For this test, contrast medium is injected directly from the bladder into the ureters through the cystoscope. The contrast medium allows the doctor to check for blockages or tumors.
Ultrasound scanning. Ultrasound scanning (also called ultrasonography or a "sonogram") is an imaging technique that allows doctors to see the outline and the interior of the kidneys and, to a lesser extent, the bladder. This procedure offers a noninvasive method of distinguishing between cysts and tumors of the kidney, checking for urinary tract obstruction, detecting inflammation and fluid collection around the kidneys, and identifying the best location for a planned biopsy.
Computed tomography (CT) scanning. CT scanning is a diagnostic technique that uses a computer and low-dose X rays to produce detailed cross-sectional images of body tissues that are displayed on a video monitor. This technique is 299
performed with or without a contrast medium (a dye) to detect stones and Urinary tumors in the urinary tract. Tract
• Magnetic resonance imaging (MRI). MRI is a diagnostic technique that uses a computer, a powerful magnetic field, and radio waves to produce detailed two-and three-dimensional images of body tissues that are displayed on a video monitor. This technique is used to detect tumors in the kidneys and bladder.
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