Vesicoureteral reflux (VUR) is a condition where urine flows backward from the bladder up toward the kidneys instead of moving in one direction out of the body. It primarily affects infants and young children, showing up in 30% to 50% of children who develop a urinary tract infection. The condition ranges from mild to severe and, when left unmanaged, can cause permanent kidney damage.
How the Bladder Normally Prevents Backflow
The ureters, the two tubes that carry urine from the kidneys to the bladder, connect at an angle and pass through the bladder wall for a short distance before opening inside the bladder. This tunnel-like segment acts as a one-way valve. As the bladder fills and pressure builds, that pressure pushes against the roof of the tunnel, compressing it shut. Anything that raises bladder pressure, such as coughing, sneezing, straining, or urinating, triggers a matching increase in compression on that tunnel, keeping it sealed.
In children with VUR, this tunnel is too short. The ureter connects to the bladder at an abnormally steep, high, or lateral angle, so there isn’t enough length for the compression mechanism to work. When bladder pressure rises, the tunnel can’t close completely, and urine pushes back up toward the kidney.
Primary vs. Secondary VUR
Primary VUR is the most common form. It’s a structural problem present from birth: the intramural tunnel simply developed too short during fetal growth. This happens because the ureteral bud, the embryonic tissue that forms the ureter, sprouts earlier or in a slightly wrong position during development.
Secondary VUR develops when something else raises bladder pressure beyond what a normal valve can handle. Bladder outlet obstruction, neurological conditions affecting bladder function, or severe bladder dysfunction can all create enough pressure to force urine backward through an otherwise adequate valve.
Symptoms in Infants and Older Children
VUR itself doesn’t always produce obvious symptoms. It’s usually discovered after a child develops a urinary tract infection, which is often the first sign that something is wrong.
In infants, a UTI caused by reflux can look deceptively vague: poor weight gain, unexplained fevers, vomiting, diarrhea, loss of appetite, or unusual tiredness. Because babies can’t describe what they feel, the infection can progress before anyone suspects a urinary cause. Kidney infections in young children tend to cause general abdominal discomfort rather than the classic flank pain adults experience, making them even harder to identify early.
Older children are more likely to report recognizable urinary symptoms: pain or burning during urination, frequent urges to urinate, abdominal pain, or bedwetting. Some children with VUR experience flank or abdominal pain before or during urination even without an active infection, a pattern sometimes called sterile reflux. They may also notice they need to urinate again shortly after finishing, because urine that refluxed up to the kidney drains back down into the bladder after voiding.
In rare cases where VUR goes undetected for years, children can present with headaches from high blood pressure or signs of kidney failure, both consequences of long-term kidney scarring.
How VUR Is Diagnosed
The gold-standard test is a voiding cystourethrogram, commonly called a VCUG. During this procedure, a thin catheter is placed in the bladder, contrast dye is instilled, and X-ray images are taken as the bladder fills and as the child urinates. If dye travels back up toward the kidneys, reflux is confirmed. The images also reveal how far the urine travels and how much the ureter or kidney dilates, which determines the grade of reflux and whether one or both sides are affected.
A VCUG can feel uncomfortable for children, but it provides information no other test can match: whether reflux is present, how severe it is, and which side is involved. These details directly shape decisions about whether to monitor the condition, start preventive antibiotics, or consider surgery.
Grading: Mild Through Severe
VUR is graded on a scale from I to V based on how far urine travels backward and how much the urinary tract dilates.
- Grade I: Urine refluxes only partway up the ureter. No dilation.
- Grade II: Urine reaches all the way up to the kidney, but the ureter and the kidney’s collecting system remain normal in size.
- Grade III: The ureter is mildly dilated, and the kidney’s collecting system shows mild expansion.
- Grade IV: Moderate dilation of the ureter and kidney collecting system, with blunting of the normal cup-shaped structures inside the kidney.
- Grade V: Severe dilation throughout. The ureter is tortuous and the kidney’s internal structures are grossly distorted.
Grades I and II are considered low-grade reflux. Grades III through V are high-grade. The distinction matters because higher grades carry greater risk of kidney damage and are less likely to resolve without intervention.
Why Kidney Damage Is the Central Concern
The real danger of VUR isn’t the backflow itself. It’s what happens when infected urine reaches the kidneys. Each kidney infection can cause scarring, and repeated infections lead to cumulative damage, a condition called reflux nephropathy. Over time, scarring can reduce kidney function and contribute to high blood pressure, protein in the urine, and in severe cases, kidney failure.
Children with recurrent breakthrough infections while on preventive antibiotics are especially vulnerable to new scarring. This is why the management of VUR focuses so heavily on preventing infections rather than simply correcting the plumbing.
Treatment Options
Watchful Waiting and Preventive Antibiotics
Low-grade VUR often resolves on its own as a child grows and the ureter lengthens naturally. Research shows that low-grade reflux can persist into adolescence in some cases, and age at diagnosis doesn’t reliably predict how quickly it will resolve. Still, many children with grade I or II reflux eventually outgrow it without surgery.
For children with higher-grade reflux (grades III through V), daily low-dose antibiotics are commonly prescribed to prevent UTIs and protect the kidneys while waiting for potential spontaneous resolution. The goal is to keep the urinary tract sterile so that even if urine refluxes, it doesn’t carry bacteria to the kidneys. The effectiveness of this approach in infants with high-grade reflux and no prior infections remains an active area of clinical debate.
Endoscopic Injection
This minimally invasive procedure involves injecting a bulking material at the opening of the ureter inside the bladder, essentially creating a small mound that helps the valve close more effectively. The procedure takes about 30 minutes on average, requires only about one day in the hospital, and children typically need pain relief for fewer than two days afterward. The overall success rate for resolving or significantly improving reflux is around 67%, which is lower than open surgery but comes with a much lighter recovery. Some children need a repeat injection.
Ureteral Reimplantation Surgery
When reflux is severe, infections keep breaking through despite antibiotics, or kidney scarring is progressing, surgical reimplantation is the most definitive option. The surgeon repositions the ureter so it enters the bladder at a longer, more gradual angle, recreating the tunnel that the child’s anatomy failed to provide. Success rates are approximately 90%. The trade-off is a more significant recovery: hospital stays average about a week, and children typically need pain medication for several days. The procedure can be performed through traditional open surgery, laparoscopy, or robotic-assisted techniques, all with comparable success rates.
The Genetic Component
VUR runs strongly in families. Between 34% and 51% of siblings of a child with VUR will also have the condition, and when a parent had reflux, roughly 65% of their children are affected. About half of children with primary VUR come from families where at least one other member has it. Because of this high familial rate, screening siblings of affected children is a common practice, even if those siblings have never had a UTI. Catching reflux before infections occur gives families the chance to start preventive measures early, before any kidney damage happens.