Finding the right tests…
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Finding the right tests…
X-Ray
MCU stands for micturating cystourethrogram, also called a voiding cystourethrogram. A thin catheter is passed through your urethra into your bladder, contrast is used to fill the bladder, and then x-rays are taken while you urinate with the catheter removed. This captures your urinary system in two states: a full, resting bladder and an actively emptying one. MCU is ordered most often in children with repeated urinary tract infections, to check for vesicoureteral reflux, a backward flow of urine from the bladder toward a kidney during voiding. It's also used to look at bladder shape, urethral narrowing, and how completely the bladder empties.
MCU shows whether urine flows backward up one or both ureters toward the kidneys while you void, and if so, how far up it travels, a grading doctors use to judge severity. It also outlines bladder shape and capacity, and shows whether the urethra narrows or the bladder empties fully. These findings guide whether reflux needs monitoring, medicine, or surgery.
MCU is built to catch a problem that only shows up under pressure: reflux that happens as the bladder squeezes to empty, not while it's simply sitting full. That's why the study has two parts. Filling the bladder with contrast through a catheter shows its resting shape and capacity. Removing the catheter and imaging while you actually urinate shows what happens under the pressure of voiding, which is when reflux is most likely to appear.
Urine that flows backward into a ureter or kidney during voiding can carry bacteria upward, which is why recurrent urinary tract infections in children, especially younger ones, are commonly followed up with MCU. Catching reflux early lets a doctor decide whether it needs watching, antibiotics, or a surgical fix before it damages a kidney.
MCU pushes contrast in through the urethra to fill the bladder, then watches the bladder empty on its own during normal urination. This voiding phase is what separates it from a retrograde urethrogram, where contrast is pushed in the opposite direction, into the urethra alone, without ever filling or emptying the bladder, a test used for a different problem, urethral injury or narrowing, rather than reflux.
It's most commonly done in children, especially after repeated urinary tract infections, but adults with certain bladder or reflux concerns can also have this test. Your doctor decides based on your symptoms.
Yes, a thin catheter is passed through the urethra to fill the bladder with contrast, then removed before your child urinates for the voiding part of the study. The catheter placement is usually the most uncomfortable part.
Most children feel some discomfort during catheter placement and while the bladder fills, but it isn't usually described as severely painful. Centres experienced in pediatric imaging take steps to keep children calm during the test.
It means urine is flowing backward from the bladder toward a kidney instead of only downward and out, which can happen during voiding. Your doctor grades its severity from the MCU images and decides on monitoring, medicine, or surgery.
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.
Generally, doctors prefer to treat an active infection first, since it's usually asked that the infection has cleared before this test. Ask your doctor or the centre for guidance in your child's case.
An ultrasound shows kidney and bladder structure without contrast or voiding, but it can't reliably catch reflux happening only during urination. MCU is designed specifically to capture that voiding-phase backward flow.
Some children with reflux are followed with repeat studies over time to see whether it's improving, staying the same, or resolving as they grow. Your doctor will advise on follow-up based on the initial grade found.