Updated

Duty to his country called U.S. Army Specialist Ricky Glenn Henderson to Afghanistan. Now duty to his family is calling him back to Texas, where he hopes to donate a majority of his liver to his dying Vietnam Vet grandfather.

Henderson flew back from Afghanistan last week determined to give the gift of life to his very sick 62-year-old- grandfather, Rickey Homer.

"The loss and the regret of me not doing anything would have outweighed this. I'm the firstborn grandson; I carry my grandfather's name," Henderson told KLTV, the ABC affiliate in East Texas.

Henderson arranged with his commanding officer to be flown back from Afghanistan to Baylor University Medical Center in Dallas to be tested as a match. He began undergoing the tests Wednesday. If he is a match, he will donate 60 percent of his own liver to Homer.

“I don’t want to look back and say, ‘Hey, I could have done something,’” Henderson told ABCNews.com.

The 21-year-old soldier told his granddad what he intended to do in a call from Afghanistan. Homer was shocked.

“He’s like, ‘Why? You’re young,’” Henderson said. “I had to sit there and explain, ‘You’re my granddad. I want to do this. You still have stuff that you need to be around for.’”

That includes being around for more fishing trips, the grandson said.

Homer, of Longview, Texas, spent four years in the Marines and 16 in the U.S. Army. He fought for his country in Vietnam, surviving fierce fighting.

He could have spent years on a donor list but without any guarantee of being a liver recipient.

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Homer has a genetic disorder called hemochromatosis, which causes cirrhosis of the liver. “The only time I've got left is what the good Lord gives me," Homer told KLTV.

Glenn's mother, Mindy Odle, said one of the doctors tried to talk her son out of it.

"I'm so proud,” she said of her son.

Dr. Giulino Testa, who directs the living liver transplant program at Baylor, told ABC.com that he found an abnormality in Henderson’s platelet count and needs to be absolutely sure the liver donation will be safe before giving it the go-ahead. If the transplant happens, he added, Henderson’s liver will return to normal size within a few days and normal function within a few months.

Homer calls his grandson his hero.

"People don't understand what a hero is until something like this happens," he said.

For Henderson it is all about serving your country and your family.

"I don't really see myself as a hero. You do what you do for the ones you love," he said.