How are kidney stones diagnosed?
Diagnosis of renal stone disease involves a medical history, physical examination, laboratory evaluation, and imaging tests. The physician determines if the patient has a history of kidney stones, documents past medical conditions, and evaluates present symptoms. Physical examination may be difficult if the patient is experiencing severe pain and is unable to remain still. Lightly tapping on the kidney region often worsens the pain. Fever may indicate a urinary tract infection that requires antibiotics.
Laboratory tests include urinalysis to detect the presence of blood (hematuria) and bacteria (bacteriuria) in the urine. Other tests include blood tests for creatinine (to evaluate kidney function), BUN and electrolytes (to detect dehydration), calcium (to detect hyperparathyroidism), and a complete blood count (CBC; to detect infection).
Diagnostic steps for kidney stones include the following steps. Establish the presence or absence of kidney stones as soon as possible so that pain management can begin if necessary. (Use physical examination, imaging techniques.) If a kidney stone is present, determine whether the stone is obstructing the urinary tract. (Use imaging techniques.) Determine the substance forming the crystal so that appropriate treatment and preventive measures can be taken. (Urine and blood tests.) There is some question about the value of identifying the stone properties in people who have had only one attack. Some experts argue, however, that because of the high risk for recurrence, analyzing the stone from even a single attack may help prevent subsequent ones. Most physicians, though, delay detailed diagnostic evaluations until a stone recurs or grows in size. Determine any metabolic abnormalities in people with recurrent stones. (Tests for urine and blood chemistries). According to a 2000 study, only 35% of patients with recurrent stones are given such tests.
Imaging tests used to diagnose kidney stones include ultrasound, intravenous pyelogram (IVP), retrograde pyelogram, and computerized tomography (CT) scan.
Ultrasound. This test uses high-frequency sound waves to produce pictures of internal structures (e.g., organs, kidney stones). Ultrasound can detect a dilated (stretched) upper urinary tract and kidney caused by a stone lodged in the ureter, but usually cannot detect small stones, especially those located outside the kidney. It is the preferred imaging method for kidney stone patients who are pregnant.
Intravenous Pyelogram (IVP). This test involves taking a series of x-rays after injecting a contrast agent (dye) into a vein. The contrast agent flows through the veins, is excreted by the kidneys, and improves the x-ray images of the kidneys and ureters. If a kidney stone is blocking a ureter, the contrast agent builds up in the affected kidney and is excreted more slowly. Most kidney stones (e.g., calcium stones) can be precisely located using this procedure. There is a slight risk for an allergic reaction to the contrast agent during this procedure and overall kidney function must be normal. IVP can take a very long time if the blockage to the kidney is severe.
# Retrograde Pyelogram. A cystoscopy (i.e., a procedure in which a telescopic instrument is inserted into the urethra) is performed to locate the opening from the ureter to the bladder. The contrast agent is injected directly into this opening and an x-ray is taken to locate the kidney stone. This procedure eliminates the risk for an allergic reaction to the contrast agent because the dye does not reach the bloodstream, but it may require anesthesia. While retrograde pyelogram is the most reliable method for visualizing the urinary system and detecting stones, it is generally used only when other imaging methods are inadequate or unsuccessful.
CT (Computerized Tomography) Scan. This test uses a scanner and a computer to create images of the urinary system. It is performed quickly but may have difficulty detecting small stones located near the bladder. CT scan can also help identify medical conditions (e.g., ruptured appendix, bowel obstruction) that cause symptoms similar to kidney stones. Newer scanners do not require a contrast agent. The non-contrast CT scan is the most common imaging test used to evaluate a possible kidney stone attack. If any stones are found, a plain abdominal x-ray is also taken to determine their size, shape, and orientation. X-rays are used for follow-up studies to monitor the stones progress.
Blood Tests for Stone Factors. Blood tests may help determine levels of blood urea nitrogen, creatinine, calcium, phosphate, and uric acid for patients with known or suspected calcium oxalate stones. These tests are often scheduled about six weeks after the attack, particularly with recurrent stones, in order to measure these substances when the stone has been passed and the patient has been stabilized. Parathyroid Tests. Tests to detect parathyroid hormone levels are administered if the physician suspects hyperparathyroidism based on other signs and symptoms. Tests for Infection. A test result that shows a high white blood cell count might indicate infection, but such results could be misleading, since white cells could also increase in response to the extreme physical stress of a kidney stone attack.
Urine samples are required to evaluate features of the urine, including its acidity, the presence of red or white blood cells, whether infection is present, any crystals, and elevated or decreased components that inhibit or promote stone formation. Clean-Catch Urine Sample for Culturing. Once it has been determined that a kidney stone is present, the patient is usually given a collection kit, including filters, to try to catch the stone or gravel as it passes out. A clean-catch urine sample is almost always required for culturing.
Urine tests that are used to determine the specific chemical and biologic factors causing the stone should be performed about six weeks after the attack, since the attack itself may change the levels of such substances, including calcium, phosphate, and citrate. It should be noted that calcium levels in the urine may be abnormal even in many people without stones. In addition, high urinary concentrations of calcium may pose a greater or lesser risk depending on age.
More information on kidney stones
What are kidney stones? - Kidney stones are solid accretions (crystals) of dissolved minerals in urine found inside the kidneys or ureters. Also known as nephrolithiasis, urolithiasis or renal calculi.
What are kidney stones made of? - Kidney stones consist of a center that consists of crystal-like substances, and a surrounding region that is composed of layers. Kidney stones are composed of different chemical substances.
What are the symptoms of kidney stones? - Symptoms often occur when a stone migrates into the ureter, the tube that carries urine from the kidney to the bladder, and prevents the drainage of urine from the kidney.
What causes kidney stones? - The development of the stones is related to decreased urine volume or increased excretion of stone-forming components such as calcium, oxalate, urate, cystine, xanthine, and phosphate.
What are the risk factors for kidney stones? - Kidney stones affect about 12% of men and 5% of women by the time they are 70 years old. Kidney stones that strike women are more apt to occur during pregnancy.
How are kidney stones diagnosed? - Diagnosis of renal stone disease involves a medical history, physical examination, laboratory evaluation, and imaging tests.
What're treatment options for kidney stones? - Treatments of kidney stones include dietary modifications (including the advice to drink plenty of water), medications, and use of a lithotriptor.
What drug treatments are available for treatment and prevention of kidney stones? - Diuretics are commonly used in the treatment of high blood pressure and other disorders to eliminate fluid and sodium from the body. Citrate salts are often given to people with calcium oxalate or uric acid stones.
What dietary factors and lifestyle measures are used for prevention of kidney stones? - The most important recommendations for reducing the risk for calcium stones are increasing fluid intake, restricting sodium, and reducing protein intake.