Calcium stones; Nephrolithiasis
The doctor will perform a physical exam. This includes pressing against the abdomen for tender locations that might indicate the presence of the stone.
The patient's age is a significant factor. Kidney stones that occur in children and young patients are more apt to result from inherited problems that cause cystine, xanthine, or, in some cases, calcium oxalate stones. In adult patients, calcium stones are most common.
A medical history may help predict which crystal has formed the stone. The doctor will need to know the following:
Many conditions can cause symptoms similar to kidney stones. Usually the diagnosis is easily made because of the specific nature of the symptoms, but it is not always clear. Urinary tract infections can cause similar, but usually less intense, pain. In fact, infection may be present with a kidney stone. Other causes of pain that may mimic kidney stones include:
Various imaging techniques are helpful in determining the presence of kidney stones. The best approach uses spiral (or helical) computed tomography scans. If these scans are not available, the patient will need ultrasound or standard x-rays. If no stones show up, but the patient has severe pain that suggests the presence of kidney stones, the next step is an intravenous pyelogram.
X-Rays. A standard x-ray of the kidneys, ureters, and bladder may be a good first step for identifying stones, since many are visible on x-rays. Calcium stones can be identified on x-rays by their white color. Cystine crystals can also show up on x-rays.
Spiral (or Helical) Computed Tomography. A type of computed tomography (CT) scan called a spiral or helical CT scan is currently the best method for diagnosing stones in either the kidneys or the ureters. This test is fast, does not require instruments or foreign chemicals to enter the body, and provides detailed accurate images of even very small stones. If stones are not present, a spiral CT scan can often identify other causes of pain in the kidney area. It is better than x-rays, ultrasound, and intravenous pyelogram -- the previous standard test for detecting kidney stones. Experts hope spiral CT will eventually be able to identify the chemicals present in a stone.
Ultrasound. Ultrasound can detect clear uric acid stones and obstruction in the urinary tract. It is not useful for finding very small stones, but some research indicates that it may be a useful first diagnostic step in the emergency room to help predict the likelihood of a stone, including suspected stones in children.
Intravenous Pyelogram. With intravenous pyelogram (IVP), the doctor injects a special dye into the patient. A technician will then take x-rays as the dye enters the kidneys and travels down the urinary tract. IVP is invasive but, until recently, was the most cost-effective method for detecting stones. Where it is available, spiral CT is now preferred, since it gives a faster diagnosis and is more accurate, safer, and similar in cost.
IVP should not be used on patients with kidney failure. There is also a risk for an allergic reaction to standard dyes, although newer, less allergenic ones are becoming available.
Magnetic Resonance Imaging. Magnetic resonance imaging (MRI) techniques are showing promise for diagnosing urinary tract obstruction but do not yet accurately reveal small stones, or ones that do not cause a blockage. Because no radiation is involved with MRI, however, it may prove to be a good option for pregnant women.
Urine samples are required to evaluate features of the urine, including its acidity and the presence of:
Clean-Catch Urine Sample for Culturing. After determining that a kidney stone is present, the health care provider usually gives the patient a collection kit, including filters, to try to catch the stone or gravel as it passes out. The urine may also be tested (cultured) for the presence of infection-causing organisms. A clean-catch urine sample is almost always required for culturing. To provide a clean catch, do the following:
Twenty-Four Hour Urine Collection. A 24-hour urine collection may be needed to measure urine volume and levels of acidity, calcium, sodium, uric acid, oxalate, citrate, and creatinine.
Urine tests that are used to determine the specific chemical and biological factors causing the stone should be performed about 6 weeks after the attack, since the attack itself may change the levels of such substances, including calcium, phosphate, and citrate.
Note that calcium levels in the urine may be abnormal even in many people who do not have stones. In addition, high urinary concentrations of calcium may pose a greater or lesser risk, depending on a person's age.
The kidney stones obtained from the urine sample are examined under a microscope. The crystal formations are often specific enough so that the doctor is able to identify the substance causing the stone.
Testing whether urine is acidic or alkaline helps to identify the specific type of stone. The levels of acidity or alkalinity in any solution, including urine, are indicated by the pH scale:
AA dipstick test for blood in the urine (called hematuria) is typically performed when patients appear in the emergency room with flank pain (the primary symptom of kidney stones). About a third of kidney stone patients, however, do not show blood in the urine, so other tests may be needed.
Blood Tests for Stone Factors. Blood and urine tests help determine what substances formed the crystals. This allows the doctor to determine the appropriate treatment and preventive measures.
Blood tests may help determine blood levels of urea nitrogen, creatinine, calcium, phosphate, and uric acid for patients with known or suspected calcium oxalate stones. Doctors will usually schedule these tests about 6 weeks after the attack, in order to measure these substances when the stone has been passed and the patient has been stabilized. This is particularly true in patients with recurrent stones.
Parathyroid Tests. Tests to detect parathyroid hormone levels are given if the doctor 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. Such results, however, could be misleading, since the number of white blood cells could also increase in response to the extreme physical stress of a kidney stone attack.
Tests for Metabolic Problems. About half of children with stones have an identifiable metabolic disorder, which increases their risk of stone recurrence five-fold. Experts argue whether tests for metabolic disorders are routinely needed once the stone composition has been determined. Studies suggest the following:
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