X-ray machines use electromagnetic energy beams to generate images of the body's internal tissues, organs, and bones. X-ray particles pass through the tissues of the body and onto a special plate similar to the film of a camera. The resulting images help doctors diagnose conditions or diseases, including those associated with the urinary tract.

Dense materials, like bone, show up as white while air appears black. Fluid, fat, and muscle are various shades of gray.

Types of X-ray Tests

A few different X-ray tests can be used to examine the urinary tract, including:

  • KUB X-ray: This type of X-ray evaluates the kidney, ureter, and bladder and is often the first diagnostic test a urologist orders.

  • Fluoroscopy: A urodynamic study that uses X-rays to capture real-time, moving images of the bladder and bladder neck. This test is often performed while a patient is urinating.

Special Types of X-ray Tests

The soft tissues of the bladder, kidneys, and ureter don’t always appear well on basic X-rays. In order to make these structures visible, a dye (contrast agent) is either injected into a vein or directly into the organ. The liquid traces, highlights, or fills in areas of the body so that they are more clearly visible on film. There are two tests that utilize contrast agents:

  • Intravenous pyelogram (IVP): The contrast dye—administered intravenously— travels through the blood, eventually making its way through the kidneys, ureters, and bladder. X-ray images are taken at various times to see how well the kidneys remove the dye, as well as how it collects in the urine. This test can identify kidney and bladder stones, an enlarged prostate, kidney cysts, or urinary tract tumors.
  • Voiding cystourethrogram (VCUG): During this test, a tube inserted into the urethra and up to the bladder transports the dye. X-ray images are taken of the bladder while it is full of the contrast agent and also during urination. A voiding cystourethrogram can identify blockages (such as kidney stones) or other problems (such as a neurogenic bladder).

When Are X-rays Used in Urology?

If urological symptoms and conditions arise, an X-ray may be used to determine the source of the problem.

Symptoms include:

  • Being unable to empty the bladder completely
  • Backed up urinary flow due to a blockage (such as kidney stones or bladder stones)
  • Abdominal swelling or mass
  • Lower back or groin pain

Conditions include:

  • Small bladder capacity
  • Urinary retention (inability to urinate completely)
  • Urinary reflux (backwards flow of urine)
  • Kidney diseases
  • Urinary tract tumors and blockages
  • Enlarged prostate

What Risks Are Associated with X-rays?

Though overexposure to radiation can cause cell mutations that result in cancer, the radiation dose of an X-ray exam are so minimal that cell damage is unlikely to occur.

Contrast agents increase the risk of side-effects, which include feeling warm, flushed, lightheaded, nauseous, or itchy and may cause hives or a metallic taste in the mouth. Rarely, the dye can cause anaphylactic shock, cardiac arrest, and a severe drop in blood pressure.

Women who are pregnant, or think they might be, should inform their physician before an X-ray test. While X-rays during pregnancy are generally considered safe, there may be other non-radiation based alternatives (such as MRI and ultrasound). Exposure to too much radiation during pregnancy may slightly increase the risk of birth defects.


Imaging of the Urinary Tract. (2012). National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). NIH Publication No. 12–5107

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