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X-Ray
RGU stands for retrograde urethrogram, an x-ray study of the urethra, the tube that carries urine out of the body. Contrast is injected backward, from the outer opening of the urethra inward, rather than filling the bladder first and imaging outward the way a voiding study does. RGU is used mainly after pelvic trauma, a straddle injury, or when blood appears at the urethral opening, to check whether the urethra has been torn or ruptured. It's also used to evaluate urethral stricture, a narrowing usually caused by scarring from injury, infection, or a past procedure. Finding a leak of contrast outside the urethra's normal path is the key sign doctors look for.
RGU shows the length, caliber, and continuity of the urethra as contrast passes through it. A narrowed segment points to a stricture, while contrast leaking outside the expected outline points to a tear or rupture. The location and extent of any leak or narrowing guides whether treatment can wait or needs urgent surgical attention.
RGU is named for the direction contrast travels: retrograde, meaning backward, pushed in from the urethral opening rather than arriving from the bladder side. That direction is chosen deliberately, because the clinical questions RGU answers are about the urethra itself, not about what happens after the bladder fills or empties.
After a pelvic fracture or a straddle injury, blood at the urethral opening is treated as a warning sign of possible urethral injury. Doctors are taught to avoid blindly passing a catheter in that situation, since forcing a catheter through a torn urethra can worsen the injury; RGU is used instead to see whether the urethra is intact before any catheter is attempted. A break in the urethra shows up as contrast leaking outside its normal course, which tells the surgical team where the injury is before they operate.
RGU never involves the bladder filling or emptying; contrast goes in one direction, from the outer opening inward, and the study is read from that single pass. A voiding cystourethrogram, by contrast, fills the bladder through a catheter and images it while it empties naturally, and is used for backward flow of urine toward the kidneys, a different question from urethral injury or narrowing.
If a urethral injury is suspected, especially after trauma, forcing a catheter through blindly can worsen a tear. RGU checks whether the urethra is intact first, so a catheter or other treatment can be planned safely.
No, it's also used to evaluate urethral stricture, a narrowing that can develop from past infection, a previous procedure, or scarring, even without a recent injury.
Injecting contrast into the urethra can cause brief discomfort or a burning sensation. It usually passes quickly once the injection is complete.
RGU pushes contrast backward into the urethra alone and never involves the bladder. MCU fills the bladder through a catheter and images it during voiding, and is used for a different problem, reflux of urine toward the kidneys.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
It's a sign of a tear or rupture in the urethral wall. Your doctor will use the location and extent of the leak to plan repair.
It's far more commonly performed in men, since the male urethra is longer and more prone to traumatic injury and stricture. It's rarely needed in women for this reason.
Some doctors prescribe a short course as a precaution since a catheter and contrast are introduced into the urinary tract. Ask your doctor or the centre about their usual practice.