What Are Kidney Stones?

Kidney stones are hard accumulations of crystallized minerals and salts that form in the kidneys. A kidney stone can also be called a nephrolith or a renal calculus, and having kidney stones is sometimes referred to as nephrolithiasis or urolithiasis.

Around 11% of males and 6% of females in the United States are estimated to have kidney stones at some point during their life. While more common in adults, kidney stones can also affect children. They are more common in people who do not drink enough fluids, have certain dietary habits, or use medications that can contribute to stone formation.

Kidney stones can be extremely small, like specks of dust or sand, but can also become as large as a golf ball in extreme cases. Kidney stones vary in shape from smooth to jagged.

After forming in the kidneys, these stones move through the urinary system where they may continue to grow. Most of the time, especially when they are small, kidney stones are removed from the body in urine without any symptoms. Larger kidney stones may irritate or block the urinary tract, which can cause pain and disrupt normal urination.

The most common symptom of kidney stones is an intense pain, known as renal colic, that can affect various parts of the abdomen, back, and pelvis. Many patients with kidney stones have blood in their urine or urine that appears cloudy. Symptoms may also include changes to the smell of urine, difficulty urinating, nausea and vomiting, and sometimes fever and chills.

Because kidney stones can cause serious symptoms and other health complications, very large stones may require treatment to break them up or to surgically remove them from the urinary tract.

Different minerals can collect to form kidney stones. Identifying the composition of stones can affect treatment and follow-up care. There are four main kinds of kidney stones:

  • Calcium stones: About 85% of kidney stones are in the category of calcium stones, which includes types known as calcium oxalate and calcium phosphate stones.
  • Uric acid stones: These stones form when there is too much of a compound called uric acid in the urine. About 10% of kidney stones are uric acid stones.
  • Cystine stones: These stones, which make up about 2% of kidney stones, occur in people who have an inherited disorder called cystinuria that leads to high levels of a specific amino acid in the urine.
  • Struvite stones: These stones are the least common of the four main types and typically occur in people who have urinary tract infections (UTIs).

While stones initially form in the kidney, they can also move into and keep growing in other parts of the urinary tract such as the bladder or the ureters. The ureters are the tubes that carry urine from the kidney to the bladder. If they are located in these areas, stones may be referred to as ureteral stones or bladder stones.

The Role of Kidney Stone Tests

Kidney stone testing has several potential purposes including diagnosis, evaluating the severity of the condition, tailoring treatment, and planning follow-up care to prevent and monitor recurrences of kidney stones:

  • Diagnosis is the process of finding the cause of a patient’s symptoms. In patients with signs or symptoms of kidney stones, tests can look to see whether stones are present. In some cases, tests can also identify the type of kidney stone. These tests can be an important part of distinguishing between kidney stones and other conditions that may cause similar symptoms.
  • Evaluating the severity of kidney stones involves looking for blockages in the urinary tract and other potential complications of kidney stones. This testing may also gather information about the size, shape, location, and composition of a kidney stone.
  • Tailoring treatment is the way that the doctor selects the best approach for each patient. This includes looking at tests that show the size and location of a kidney stone in order to determine if it will pass on its own or if steps are necessary to remove it or break it up.
  • Planning follow-up care is important for people who have had a kidney stone. Testing can be used to periodically check for new stones. Tests can also help determine why a stone formed, and this may help patients take steps to reduce the risk of future kidney stones.

A health care provider is in the best position to explain the purpose of any specific test and how it will be used in the diagnosis or medical care of kidney stones.

Who should get testing?

Kidney stone testing is typically only done in people who have symptoms that could be caused by kidney stones or in people who have had kidney stones before.

Since kidney stones can affect people of any age, testing may be appropriate in anyone who has symptoms. Testing is prescribed by a health professional, so talk to a doctor if you have symptoms of a kidney stone such as:

  • Significant pain in your abdomen, back, side, or groin
  • Blood in your urine
  • Urine that appears grainy or cloudy
  • Changes to the color or smell of your urine
  • Difficulty urinating
  • Nausea and vomiting
  • Chills and/or fever

Testing is also often recommended if you have previously been diagnosed with a kidney stone. Specific tests may be performed to learn more about the type of kidney stone you had, detect other stones, and guide preventive steps to decrease the chances of future kidney stones.

Getting test results

The results of kidney stone testing will normally be provided by your doctor. In some cases, a doctor who specializes in conditions of the urinary tract, called a urologist, may be involved in your care and deliver test results.

The timeframe for receiving test results depends on the purpose of testing and the type of tests performed. Some tests can provide results almost immediately while others may take a few business days.

Frequently, the diagnosis and management of kidney stones requires more than one test. As a result, the doctor may need to receive all of the test results before being able to explain their overall significance in your situation.

If a kidney stone is diagnosed, your doctor will discuss whether any treatment is necessary so that the stone can pass without causing a blockage in your urinary tract. They may also review options for reducing your symptoms or preventing complications. If no kidney stone is found, other tests may be needed to determine the cause of your symptoms.

Types of Kidney Stone Tests

Many different types of tests can be used to diagnose kidney stones and plan treatment. In most cases, this involves a combination of a review of your medical history, a physical exam, urine and blood tests, and imaging tests.

The following sections provide details about these different categories of kidney stone tests.

Medical history and physical exam

If you have symptoms of kidney stones, your doctor may begin by discussing your symptoms and asking about other aspects of your health. A physical exam may then be performed to look for other possible causes of your symptoms.

Obtaining this information can help the doctor evaluate whether a kidney stone is a likely explanation for your symptoms. Most often, the physical exam and review of your health history are just the first step in reaching a definitive diagnosis. In some cases, especially if you have had kidney stones before, this initial examination may be enough for the doctor to diagnose a kidney stone.

Imaging tests

Imaging tests are often used in diagnosing kidney stones because they allow the doctor to see if a stone is present. Imaging tests can also help determine the location of a stone and provide information about its shape, size, and composition.

Computed tomography (CT) scans are the most commonly used imaging test for detecting kidney stones. CT scans of your abdomen and pelvis combine multiple x-ray images to provide a 3D picture of your urinary tract. This is generally considered to be the most accurate and useful imaging test for visualizing kidney stones.

With this detailed image, the doctor may see a kidney stone and where it is located. The scan may also show the size of the stone, if there are any urinary blockages, and if there are other conditions that could be causing your symptoms.

Because they involve multiple x-ray images, CT scans involve exposure to low levels of radiation. While this is considered safe for most people, CT scans may not be recommended for some patients such as pregnant people and children.

Abdominal ultrasound is another imaging test that can help show stones in the urinary tract. A benefit to ultrasound is that it does not expose a patient to any radiation.

While an ultrasound can detect many kidney stones, it is not as reliable as a CT scan in showing stones and their location. As a result, ultrasound is most often used in specific circumstances, such as:

  • When a CT scan is not available
  • When it is necessary to limit a patient’s radiation exposure, including in children, pregnant people, and people who may need multiple imaging tests
  • When a patient is in the emergency room and bedside ultrasound can be performed quickly to assess their situation and help determine if a CT scan is needed

Other imaging tests may be performed to detect some kidney stones but are much less commonly used. Examples of less commonly used imaging tests are abdominal x-rays with or without a contrast material, magnetic resonance imaging (MRI), and digital tomosynthesis.

Urine testing

Urinalysis is a form of urine testing and is commonly used to diagnose and assess kidney stones. Urinalysis can include various measurements and assessments of a urine sample. For kidney stone testing, urinalysis often looks for:

  • Microscopic traces of blood in the urine
  • Abnormalities in urine’s acidity or pH level
  • Irregular levels of certain minerals that are associated with kidney stones
  • Signs of a urinary tract infection

Testing may be conducted with a one-time urine sample provided at a doctor’s office or hospital. In some situations, urinalysis may require a 24-hour urine collection so that all of the urine produced during a day can be analyzed.

Blood tests

Blood tests that use a sample of blood drawn from a vein in the arm may be ordered to evaluate how well the kidneys are working. Blood tests can also measure several minerals, known as electrolytes, that can be related to the formation of kidney stones.

Commonly used blood tests for kidney stone diagnosis are the basic metabolic panel (BMP) or the comprehensive metabolic panel (CMP) and the uric acid test.

Testing after a kidney stone is diagnosed

Additional testing is usually recommended after a kidney stone has been diagnosed.

If a person is known to have a kidney stone, they are usually encouraged to strain their urine through a filter so that the stone can be collected when it passes. This can confirm that it is no longer in the body and also allows a laboratory to analyze the stone’s composition.

Identifying the type of stone can help the doctor understand why it formed in the first place. Determining the cause of kidney stones can be used to recommend steps to prevent future kidney stones.

Other evaluations that may be used to assess the risk of future kidney stones include:

  • A focused health history review: This is designed to identify elements of a person’s family history, lifestyle and dietary habits, and/or medications that may contribute to the risk of developing kidney stones.
  • Imaging tests: Depending on the imaging that was done for the initial diagnosis, the doctor may recommend using a CT scan or other test to look for stones that remain in the urinary tract. Periodic imaging may be performed as a way to monitor for new kidney stones.
  • Urinalysis: Follow-up testing can involve one or more 24-hour urine collections to analyze the amount of urine that a patient produces, its acidity, and its levels of various minerals. This testing is typically done at least a couple of months after a kidney stone has passed and symptoms have resolved.
  • Blood testing: Bloodwork, such as a full renal function panel, may check for levels of calcium and other minerals in the blood, which can help identify health conditions that may be related to kidney stones.

Not all people who have had a kidney stone take these tests. Instead, doctors will consider multiple factors, including the risk of recurrent kidney stones, to determine the most appropriate set of tests for each individual.

Getting Tested for Kidney Stones

Kidney stone testing is ordered by a doctor after evaluating your specific situation. When recommended, the testing is typically performed in a doctor’s office or hospital.

If you have symptoms of kidney stones, it is important to promptly contact a health care provider for medical advice about the most appropriate testing and where it can be conducted.

At-home testing

No at-home test is available that can dependably detect or diagnose kidney stones. Testing is performed by a health care professional in a medical setting.

Comparing Tests

Comparing kidney stone testing in children and adults

Kidney stones are more common in adults but can also occur in children of any age. In general, kidney stone testing is similar in adults and children. Tests typically include a physical exam, a review of symptoms, imaging, urinalysis, and blood tests.

The biggest difference in kidney stone testing in children and adults is that ultrasound is more frequently used as the initial form of imaging in children. This is done to reduce a child’s exposure to the radiation from CT scanning. However, in some cases, the benefits of follow-up CT scanning after an ultrasound may be greater than the risks.

As in adults, children may have additional testing after passing a kidney stone to better understand its composition and their risks for developing kidney stones again in the future.

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