As someone who promotes health, physician Matt Grinsell didn't like the idea of telling patients to avoid playing sports like football or basketball.

But that is what many doctors suggest for the 1 in 1,500 children born with a single kidney. The fear is they could catastrophically damage the organ, leading them to need a transplant.

But while Grinsell was training in Virginia and saw a patient who was told he couldn't play contact sports because of the risk to his kidney, Grinsell started to wonder why.

"It was a hunt to find out, is there any evidence that playing contact sports is dangerous to kidneys?" he said. "Telling someone they cannot be physically active — I do not like that as a medical recommendation."

About eight years later, the nephrologist at Primary Children's Medical Center and professor at the University of Utah has published a study that shows his hunch was right.

Kidney injuries are rare, according to a study being published Monday in the journal Pediatrics. And youths who have a normal single kidney shouldn't be barred from sports.

"These patients should be allowed to participate as long as they are made aware of the risks," Grinsell said, adding that he hopes doctors will "permit more patients to follow their passion and participate in the sports they enjoy."

That's important advice to parents like Sara Gensch, whose 5-year-old son has one functioning kidney. At first, she and her husband feared they might have to move from the mountain town of Wilson, Wyo., where they love to ski, hike, bike and swim.

But after Grinsell explained that the risk of kidney injury was low, the family decided to keep living an active life.

Wolfi learned to ski at 18 months old. He hikes, rides a bike and climbs jungle gyms.

Gensch said they may teach him martial arts, so he will know how to fall while protecting himself. And he wears a rodeo vest to protect his kidneys if he falls off his bike or while skiing.

"They're going to hurt their head, they're going to break an arm before he hurts his kidney," she said. "I just need to let him be a little boy."

Grinsell, along with colleagues from the University of Virginia and West Virginia University, analyzed data from the National Athletic Trainers' Association High School Injury Surveillance Study, which was collected from 1995-97.

There were nearly 24,000 injuries among varsity athletes during games or practices of contact sports, including football, basketball, baseball, hockey and soccer.

Just 15 involved a kidney, and none of those injuries required surgery.

By comparison, there were 3,450 knee injuries, 2,000 head, neck or spine injuries and 1,200 mild traumatic brain injuries. Those injuries, the study notes, would be more debilitating than losing kidney function.

Football players were more than 100 times more likely to hurt their head, neck or spine than a kidney, according to the study.

In addition, some of the top causes for end-stage renal disease requiring a transplant are from Type 2 diabetes and chronic high blood pressure.

"I'd rather kids get out there and be active," Grinsell said.