Diagnosing vesicoureteral reflux requires specialized testing to confirm whether urine is flowing backward in the urinary tract and to determine the severity of the condition, helping doctors choose the best approach to protect your child’s kidneys from potential damage.

Introduction: When to Seek Diagnostic Testing

If your child has experienced a urinary tract infection, especially one that comes with a fever, it’s important to consider diagnostic testing for vesicoureteral reflux. This condition often remains hidden until a urinary infection brings it to light, making early detection essential for preventing complications down the road.^[3]

About one in three children who develop a urinary tract infection with fever actually have vesicoureteral reflux, though the true number may be higher since many children without symptoms never get tested.^[3] This means that urinary infections in young children should not be taken lightly, particularly when fever is present, as they may signal an underlying problem with how urine flows through the urinary system.

Children who show repeated signs of urinary trouble, such as frequent or urgent need to urinate, bedwetting after being toilet trained, accidents during the day, or a burning sensation while urinating, should also be evaluated.^[8] If your child experiences pain in the side, back, or belly along with fever and chills, these symptoms may point to a kidney infection, which can be related to reflux and requires prompt medical attention.

Sometimes vesicoureteral reflux is discovered even before a baby is born. During routine prenatal ultrasound examinations, doctors may notice that the baby’s kidneys or ureters appear swollen—a condition called hydronephrosis or urinary tract dilation. When this swelling is detected, testing after birth is recommended to check whether reflux is the underlying cause.^[8]

Family history also matters when deciding who should undergo diagnostic testing. If a brother, sister, or parent has been diagnosed with vesicoureteral reflux, there is a greater chance that other children in the family will have it too. More than one in four siblings of children with reflux will also have the condition, and more than one in three children with a parent who has reflux will develop it themselves.^[3] Because of this hereditary connection, doctors often recommend screening younger siblings of affected children, even if they have never shown symptoms of urinary tract infections.

Diagnostic Methods for Identifying Vesicoureteral Reflux

When a doctor suspects vesicoureteral reflux, several tests are used to confirm the diagnosis and understand how severe the condition is. The most important of these is a specialized X-ray test called a voiding cystourethrogram, often shortened to VCUG. This test is considered the gold standard for diagnosing reflux because it shows exactly how urine moves through the urinary system.^[5]

During a voiding cystourethrogram, a healthcare professional places a thin, flexible tube called a catheter through the urethra—the opening where urine comes out—and into the bladder. A special liquid called contrast dye is then gently filled into the bladder through the catheter. This dye shows up clearly on X-ray images, allowing doctors to see the bladder, ureters, and kidneys in detail.^[9]

While the bladder is being filled, X-ray pictures are taken to check whether any of the contrast liquid is traveling backward up the ureters toward the kidneys. Once the bladder is full, the catheter is removed and your child is asked to urinate. More X-ray images are taken during this voiding phase because reflux often happens when the bladder contracts to push out urine.^[5] The entire test typically takes between 15 and 20 minutes.

The voiding cystourethrogram is especially valuable because it not only confirms whether reflux is present but also helps doctors grade its severity. Reflux is ranked on a scale from grade one (the mildest form) to grade five (the most severe). In grade one, urine backs up only into the ureter but doesn’t reach the kidney, and the ureter remains a normal width. As the grades progress, the backflow reaches the kidney and causes increasing dilation or widening of the ureter and kidney structures.^[1]

The test can cause some discomfort, particularly from the catheter placement or from having a full bladder, but it is not usually painful. Some children may be given calming medicine called a sedative to help them stay relaxed during the procedure. There is a small risk of developing a urinary tract infection from the catheter, and the test does expose the child to a small amount of radiation.^[9]

Before the voiding cystourethrogram, doctors often perform a kidney and bladder ultrasound. This test uses sound waves to create pictures of the urinary tract and helps doctors check the overall structure of the kidneys, ureters, and bladder. Ultrasound is completely painless and doesn’t use radiation, making it a safe first step.^[8] It can reveal whether the kidneys or ureters are swollen and can detect other urinary tract abnormalities that might cause infections or kidney problems.

However, ultrasound alone cannot confirm whether vesicoureteral reflux is present. It provides an outline and general view of the organs but cannot show the backward flow of urine that defines reflux. That’s why the voiding cystourethrogram is necessary for a definitive diagnosis.^[12]

Another imaging option is a nuclear scan, also called a radioisotope scan. This test uses a small amount of radioactive material, called a tracer, that is detected by a special scanner. The scanner creates images showing how well the urinary system is working and whether reflux is occurring. Nuclear scans can be used instead of or in addition to the voiding cystourethrogram, and they expose the child to less radiation than traditional X-rays.^[9]

Blood tests and urine tests are also part of the diagnostic process. A urine test can confirm whether your child has a urinary tract infection and identify which bacteria are causing the problem. This information helps doctors choose the right antibiotic treatment. Blood tests can show how well the kidneys are working and check for signs of kidney damage or infection.^[8]

If initial tests are abnormal or if your child has had repeated infections with fever, doctors may recommend a kidney scan, also known as a renal scan. This test measures the actual function and drainage of each kidney and can reveal whether there is kidney damage or scarring from previous infections. A specific type of kidney scan called a DMSA scan uses a radioactive substance that is absorbed by healthy kidney tissue, making it especially useful for detecting scars.^[12]

Some medical centers also offer a test called a voiding urosonogram, which is similar to the voiding cystourethrogram but uses ultrasound instead of X-rays. This alternative avoids radiation exposure entirely, though it may not provide as detailed images as the traditional X-ray method.^[14]

Distinguishing vesicoureteral reflux from other urinary tract problems is an important part of the diagnostic process. Doctors look for signs of blockages, abnormal bladder function, nerve problems affecting the bladder, or other structural defects. Tests like the voiding cystourethrogram can reveal conditions such as posterior urethral valves (an abnormal fold of tissue in the urethra), ureterocele (a ballooning of the ureter where it enters the bladder), or duplication of the ureter—all of which can occur alongside reflux or mimic its symptoms.^[6]

Diagnostics for Clinical Trial Qualification

When children with vesicoureteral reflux are being considered for participation in clinical trials, specific diagnostic criteria are typically required to ensure that the study includes the right patients and produces reliable results. These criteria help researchers understand the exact nature and severity of each child’s condition.

The voiding cystourethrogram remains the primary diagnostic test used to qualify children for clinical trials involving vesicoureteral reflux. This is because it provides the most accurate and detailed information about whether reflux is present and how severe it is. Clinical trials often specify which grades of reflux are eligible for enrollment—for example, a study testing a new surgical technique might only include children with grade three, four, or five reflux.^[9]

Researchers may also require baseline kidney function tests before a child can join a trial. Blood tests measuring substances like creatinine help determine how well the kidneys are filtering waste from the blood. Urine tests may be performed to check for protein or blood in the urine, which can indicate kidney damage.

A kidney scan or DMSA scan might be required to document whether any kidney scarring exists at the start of the trial. This baseline information allows researchers to measure whether the treatment being studied prevents new scars from forming or stops existing damage from getting worse.^[12]

Kidney and bladder ultrasound is often repeated at intervals during clinical trials to monitor changes in the size of the kidneys or ureters. This non-invasive test can be performed multiple times without concerns about radiation exposure, making it ideal for tracking progress over the course of a study.

Some clinical trials may also require documentation of urinary tract infection history. Researchers may ask parents to provide detailed records of how many infections the child has had, whether they involved fever, and how they were treated. This information helps trials evaluate whether new treatments reduce the frequency of infections compared to standard care.

Eligibility for trials may also depend on whether the child has primary or secondary vesicoureteral reflux. Primary reflux, which is present from birth due to a structural problem with the ureter, is more common and may be the focus of certain studies. Secondary reflux, which develops because of blockages or nerve problems, might require different research approaches.^[1]