CT scans use a series of X-rays to see inside your body. It’s considered the gold standard for diagnosing kidney stones, but the procedure is not without some risks.

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Imaging tests play an important role in the diagnosis and treatment of kidney stones. These diagnostic tests make it possible for doctors to find the stones, see how big they are, and rule out other medical conditions.

Computed tomography (CT) scans are the gold-standard imaging technique for diagnosing kidney stones. The risks associated with a single CT scan are minimal, but CT scans do expose your body to radiation. Low dose CT scans produce less radiation, and research suggests that they’re still very accurate for diagnosing kidney stones.

Keep reading to learn more about how CT scans are used to diagnose kidney stones.

Kidney stones are hard mineral deposits that develop in your kidneys. They can cause severe pain when they block a ureter — the narrow tubes that carry urine from your kidneys to your bladder. According to the National Kidney Foundation, it’s estimated that about 1 in 10 people will have a kidney stone at some point in their life.

Doctors can often diagnose kidney stones based on your symptoms and medical history. A CT scan, also sometimes called a CAT scan, uses a series of X-rays to create an image of the inside of your body. A CT scan provides a more detailed image than traditional X-rays.

Sometimes a CT scan is performed with a contrast dye. Contrast dye is taken by mouth or given through an intravenous (IV) line in one of your veins (intravenously). It helps medical professionals see your organs more clearly. Typically, a CT scan without contrast dye is performed for diagnosing kidney stones.

Each scan can cover the area from the upper part of the kidneys to the base of your bladder. These scans can also show doctors the size of the stone and identify abnormalities in the ureters that lead from your kidneys to your bladder.

CT scans have several advantages over other imaging techniques, including:

After treatment, a CT scan can help:

  • verify that all the stones have been passed
  • rule out narrowing or inflammation of the urinary tract
  • detect possible complications

CT scans can be very accurate at identifying kidney stones. Studies have found that CT scans can correctly identify kidney stones more than 95% of the time and confirm that no kidney stones are present more than 98% of the time.

In a 2018 review of studies, researchers found that:

  • Low dose CT scans correctly identified kidney stones 90% to 98% of the time.
  • Low dose CT scans correctly confirmed no kidney stones were present 88% to 100% of the time.
  • Ultra-low dose CT scan correctly identified kidney stones 72% to 99% of the time.
  • Ultra-low dose CT scans correctly confirmed no kidney stones were present 86% to 100% of the time.

CT scan limitations include higher cost than ultrasound and higher amounts of radiation exposure than other imaging techniques.

A single CT scan is generally a very safe procedure with a low risk of complications. Some people can develop an allergic reaction to contrast dye.

The biggest risk is that CT scans expose your body to radiation, and recurrent CT scans may increase your risk of cancer. In a 2020 review of studies, researchers found that regular exposure to radiation from CT scans was associated with a 2.55 higher risk of developing thyroid cancer and 1.55 times higher risk of developing leukemia.

Ultrasound is generally preferred over CT scans for pregnant women to reduce radiation exposure to the fetus.

Low dose CT scans expose your body to less radiation and may decrease your future cancer risk.

In a 2020 review, researchers found evidence among high quality studies that low dose radiation CT scans do not increase cancer risk.

If you go to an emergency room with symptoms of a kidney stone, a doctor may give you medication to ease your pain. You may also be given medications to help with other related symptoms like nausea or vomiting.

Before your CT scan, the radiographer, the healthcare professional who will perform your CT scan, will likely ask you some questions. They may also explain what the procedure involves, which will probably be similar to the following:

  1. You’ll change into a hospital gown and remove any metal objects before entering the scanner.
  2. You’ll lie on a table that slides into a special tunnel-shaped scanner.
  3. The scanner contains a ring that rotates around your abdominal area as you pass through. You’ll hear a whirring noise when the scanner is on.
  4. A radiographer will operate the CT scanner from another room. You’ll be able to communicate with them through an intercom. You’ll need to lie very still during the procedure. You may be asked to hold your breath.
  5. The radiographer will re-enter the room and help you out of the scanner.

The scan usually takes 10 to 20 minutes. You may have to wait for 15 to 30 minutes if you had contrast dye.

CT scans and ultrasound are the two main types of imaging tests used for diagnosing kidney stones. CT scans are generally more accurate, but they expose your body to radiation.

Here’s a comparison of the accuracy and level of radiation exposure of various scans, according to a 2016 study:

Type of imaging Percentage of people with kidney stones with a correct diagnosisPercentage of people without kidney stones with a correct diagnosisRadiation (mSv)
CT scan95%98%10.0
Low dose CT scan95%97%~3.0
Kidney ureter bladder plain film radiography (X-rays)57%76%0.7

CT scans are the gold-standard imaging test for accurately diagnosing kidney stones. They’re generally safe but typically expose your body to more radiation than other types of imaging techniques.

Low radiation CT scans expose your body to less radiation than traditional CT scans. Research suggests that low radiation CT scans are still very accurate at diagnosing kidney stones.