In urology, a voiding cystourethrogram (VCUG), also micturating cystourethrogram (MCUG), is a technique for visualizing a person's urethra and urinary bladder while the person urinates (voids). The technique consists of catheterizing the person in order to fill the bladder with a radiocontrast agent, typically diatrizoic acid. Under fluoroscopy (real time x-rays) the radiologist watches the contrast enter the bladder and looks at the anatomy of the patient. If the contrast moves into the ureters and back into the kidneys, the radiologist makes the diagnosis of vesicoureteral reflux, and gives the degree of severity a score. The exam ends when the person voids while the radiologist is watching under fluoroscopy. Consumption of fluid promotes excretion of contrast media after the procedure. It is important to watch the contrast during voiding, because this is when the bladder has the most pressure, and it is most likely this is when reflux will occur.
Vesicoureteral reflux (kidney reflux) is diagnosed with an ultrasound and VCUG. Children who have recurrent urinary tract infections are given this test to determine the risk of subsequent infections causing potentially damaging kidney infections.