Definition of Reflux nephropathy:

Reflux nephropathy is a condition in which the kidneys are damaged by the backward flow of urine into the kidney.

Causes, incidence, and risk factors:

Urine flows from the kidneys, through the ureters, and into the bladder. Each ureter has a one-way valve where it enters the bladder, preventing urine from flowing back up the ureter.

Reflux nephropathy occurs when these valves fail, allowing urine to flow back up to the kidney. If the bladder is infected or the urine contains bacteria, the kidney become infected (pyelonephritis).

Because the pressure in the bladder is generally higher than in the kidney, the reflux of urine exposes the kidney to unusually high pressure. Over time, this increased pressure will damage the kidney and cause scarring.

Reflux can occur in people whose ureters do not extend very far into the bladder. The ureters enter the bladder through "tunnels" in the bladder wall, and the pressure in the bladder normally keeps these tunnels pressed closed. If the bladder-wall tunnels are short or absent, pressure within the bladder can force urine back up the ureter.

Reflux can occur with other conditions, including the following:

• Abnormal ureters
• Bladder infections (cystitis)
• Bladder outlet obstruction
• Bladder stones
• Neurogenic bladder

Reflux nephropathy is often found when a child is checked for repeat or suspicious bladder infections. If reflux is discovered, the child's siblings may also be checked, because reflux can run in families.

The degree of reflux -- separated into five different grades -- helps determine treatment. Simple reflux often falls into grade I or II.

Reflux nephropathy also can occur from temporary swelling after the ureters are reimplanted during a kidney transplant or because of trauma to the ureter.

The risk factors include a personal or family history of reflux, abnormalities of the urinary tract, and repeat urinary tract infections.