Kidney Stones

  • Diagnosis

    The doctor will perform a physical exam. This includes tapping on the back over the kidneys and pressing on the abdomen to detect tender locations.

    Medical History

    The patient's age is a significant factor. Kidney stones that occur in children and young patients are more likely to result from inherited problems that cause excess cystine, xanthine, or, in some cases, calcium oxalate. 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:

    • Any previous kidney stone attacks
    • History of cancer, sarcoidosis, or small bowel disease
    • Any medications being taken, including non-prescription substances, particularly high doses of vitamins D or C and calcium-containing antacids

    Ruling out Other Disorders

    Many conditions can cause symptoms similar to those of 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, people with an infection may also have a kidney stone.

    Other causes of pain that may mimic kidney stones include:

    • Gallstones
    • Diverticulitis (infection or irritation of abnormal pouches in the intestines)
    • Intestinal blockage
    • Blood clots
    • Irritable bowel syndrome
    • Appendicitis
    • Peptic ulcers
    • Pancreatitis (inflammation of the pancreas)
    • Hepatitis
    • Pelvic inflammatory disease
    • Inflammatory bowel disease (Crohn's and colitis)
    • Heart attack

    Imaging Techniques

    Various imaging techniques are helpful in determining the presence of kidney stones. The best approach uses spiral (or helical) computed tomography (CT) 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 (IVP).

    X-Rays. A standard x-ray of the kidneys, ureters, and bladder may be a good first step for identifying stones, because many stones 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 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, noninvasive, and it 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 IVP 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 an effective first diagnostic step in the emergency room to help identify whether a patient has a stone. Ultrasound is also effective in children.

    Intravenous Pyelogram (IVP). With IVP, the doctor injects a special dye into the patient. A technician then takes x-rays as the dye enters the kidneys and travels down the urinary tract. IVP is invasive but, until recently, it 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 dyes are becoming available.

    In the procedure intravenous pyelogram (IVP), the patient is injected with dye. X-rays are taken as the dye travels through the urinary tract. This procedure is done to confirm the presence of kidney stones, although some stones may be too small to see.

    Magnetic Resonance Imaging. Magnetic resonance imaging (MRI) techniques are showing promise for diagnosing urinary tract obstruction, but they do not yet accurately reveal small stones, or stones that do not cause a blockage. Because no radiation is involved with MRIs and ultrasounds, however, they are good options for children and pregnant women.

    Urine Tests

    Urine samples are needed to evaluate features of the urine, including its acidity and the presence of:

    • Red or white blood cells
    • Infection
    • Crystals
    • High or low levels of chemicals that inhibit or promote stone formation

    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:

    • First, wash your hands thoroughly, and then wash the penis or vulva and surrounding area four times with downward strokes, using a new soapy sponge each time.
    • Begin urinating into the toilet and stop after an ounce or two.
    • Position the container to catch the middle portion of the urine stream.
    • Urinate the remainder into the toilet.
    • Tighten the cap on the container securely, being careful not to touch the inside of the rim.
    Click the icon to see an image of a calcium urine test.

    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.

    • You should not change any of your usual eating or drinking patterns when performing this test.
    • Discard the first urination on the day of the test.
    • Afterward, collect all urine passed over the next 24 hours, including the first urination on the morning of the second day.
    • A second 24-hour urine collection may be needed to determine whether treatment is working, or it may be done if the first analysis was not conclusive and the doctor suspects a less common stone, such as a cystine or xanthine stone.
    Click the icon to see an image of a uric acid urine test.

    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 for stones, depending on a person's age.

    Microscopic Examination

    Kidney stones that are removed are sent for stone analysis (crystallography).

    Testing the Acidity of Urine

    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:

    • A pH value of 7.0 is neutral.
    • A solution with a low pH (below 7.0) is acidic. (A low pH favors the development of uric acid and cystine stones.)
    • A solution with a high pH is alkaline. (A high pH favors the development of calcium phosphate and struvite stones.)

    Testing for Blood in the Urine

    A dipstick test for blood in the urine (called hematuria) is typically performed when patients come to the emergency room with flank pain (the primary symptom of kidney stones). About a third of kidney stone patients, do not show blood in the urine, so other tests may be needed.

    Blood Tests

    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 in 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:

    • People with recurrent calcium stones have a wide range of irregular blood or urine test results, indicating a variety of possible metabolic disorders. For example, calcium stones in middle-aged women may be due to parathyroid abnormalities.
    • Calcium phosphate stones most likely result from renal tubular acidosis.
    • People with non-calcium stones generally have identifiable metabolic disorders.
    • Determining the stone composition may be sufficient for treatment, and may help avoid unnecessary metabolic tests.