Born with congenital kidney failure, Zachary Elsenpeter faced a lifetime of medical complications.

He had his first kidney transplant, from his father, as an infant. But by age 5, his body began to reject it. A buildup of antibodies fighting the kidney gave him only a 3 percent chance of finding a perfect match for a new organ.

Zachary was put on a list of more than 100,000 people waiting for a kidney. His mother, Stacey Elsenpeter, felt helpless.

“It’s the worst feeling ever as a parent,” Stacey said. “Just watching him get sicker and sicker and there’s nothing I can do but pray someone’s going to come forward to donate.”

Stacey wanted to donate her kidney to him, but she wasn’t a match for her son.

That didn’t stop her from getting proactive: She signed up for the Paired Exchange Program at the University of Minnesota Health.

“I said, ‘I’m not taking that 3 percent,’ ” Stacey said.

She wrote an e-mail to a favorite television celebrity that she hoped would change the family’s fortunes. Years later, it did.

While he was undergoing more than 70 surgeries by the age of 13, Zachary had to find a way to cope with so much hospital time. He found it in “The Ellen DeGeneres Show.”

“I’m a huge fan,” Zachary said. “She just makes me laugh, and it makes you forget that you’re sick.”

For the Elsenpeters, the show became a daily ritual that kept the laughs coming through Zachary’s medical ups and downs, which included complications with his urinary tract, bladder and bones.

More than once, Stacey wrote to the show — first to seek help finding a donor, and later, to bring awareness to the program that saved Zachary’s life. She never expected to hear back.

So her shock was understandable when DeGeneres herself patched into the family’s Andover home via video feed last month to offer them tickets to her show. Stacey jumped up and down upon seeing DeGeneres on her computer screen, shouting “This is not real!”

“I’m feeling awesome, ever since I got that kidney,” Zachary told DeGeneres in their first conversation.

DeGeneres, of course, had a hilarious response.

“This is the kind of commitment — listen to me, everybody — this is the kind of commitment I need from my viewers,” the host quipped. “Even though he’s been in and out of the hospital, he does not stop watching my show. That’s what I want, that’s what I need.”

Stacey and her three children, Zachary, Austin and Kylie, went on an all-expenses-paid trip to California this month to attend the taping, one of DeGeneres’ “12 Days of Giveaways” episodes, in which audience members win big prizes.

They each took home gift cards, airline tickets, wireless headphones and an Xbox One, but the highlight was being called up on the set to sit with DeGeneres and share their story. DeGeneres then handed Zachary a giant check for $10,000.

“We had the trip of a lifetime,” Stacey said afterward.

A paired program

Zachary was part of a paired donation program, which helps make matches among people who want to donate a kidney to a family member and can’t. Potential donors from within a family donate to a stranger in need, and that patient’s potential donor gives to another person, and so on. The chain gets tipped off by an altruistic “non-directed donor” who doesn’t have a target for their donation.

The program was launched at the U in 2009, and since then has participated in more than 80 exchanges that included the world’s longest chain of 35 transplants.

When Stacey signed up, there were no matches for Zachary. But three years later, a stranger who wanted to donate a kidney launched a chain. That person matched a patient in South Dakota who needed a kidney. And that patient’s family member matched Zach.

Stacey was the next link in the chain, donating to a teenager on the U’s kidney donation wait list.

“These were miracle matches,” said Dr. Ty Dunn, Stacey’s transplant surgeon and the director of the paired exchange program at the U. “It’s really cool that two kids benefited.”

Kickstarting donations

Six years after his kidney transplant, Zachary’s health has greatly improved. And so has his quality of life. Children who don’t have working kidneys have to be on dialysis several times a week, hours at a time. Zachary no longer has to be tied to a dialysis machine.

“We’re talking about a child missing school three times a week, kids not being able to go to slumber parties or birthday parties, and if they do, they can’t eat the pizza or drink the pop,” said Dr. Priya Verghese, Zachary’s pediatric nephrologist at the U.

Zachary’s appearance on “Ellen” highlighted for Verghese “the profound impact this [kidney exchange] program has had on his life,” she said.

Stacey, meanwhile, has become an advocate for blood and organ donation. She hopes the visibility of her family’s appearance on “Ellen” helps kickstart more chains.

“I think it’s going to change the whole world in organ donation — I just feel it,” she said.

Word is already spreading. DeGeneres posted a photo of the Elsenpeters on Instagram with the caption: “I couldn’t stop thinking about this family.” It’s gotten more than 100,000 likes.

Since joining the host on the show, Stacey says her inbox has been overflowing with e-mails from other parents who want to do what she did for her son.

She would do it all over again, if she could.

“I wish I had more kidneys to donate.”