"There's no question that by setting a default you are setting policy," said Johnson, who published the results in a recent issue of the journal Science. "There's no such thing as a neutral default on the decision to donate."
Sheldon Zink, director of the Program for Transplant Policy and Ethics at the University of Pennsylvania in Philadelphia, agrees that changing the current sign-up system could help boost donor numbers, but she says making these changes is no simple task and needs to be done with care.
"Right now we're all over the board in terms of how people can sign up," she said. "The first thing we need to do is set up a national system that is consistent in every state and then we have to make sure everyone is making an informed decision."
Even though most states enlist donor volunteers when they sign up for their driver's licenses, few states share the same policies. In California, for example, a red dot on the back of a driver's license can indicate a person's willingness to donate their organs. In Virginia, people are asked to record a yes, no or undecided when it comes to donating their organs. And in 19 other states, people are not prompted to make any decision when signing up to receive their driver's licenses.
The nature of a donor's agreement also varies by state. In some, medical workers must also receive a go ahead from family members while in others, all that's needed is a person's explicit consent before their death.
As a Catholic, the Rev. Robert Finn has his own concerns. He points out that according to Catholic doctrine, organ donation after death "is a noble and meritorious act and is to be encouraged." But he argues people must be vigilant about when they declare a person is indeed dead.
Most organ donations take place after a patient has shown irreversible loss of all brain activity. But in some 2 percent of cases, the call is made after life support is taken away and the heart stops beating for a given period of time (usually five minutes).
"We don't think there is sufficient assurance that the person is dead," said Finn, who is editor of the St. Louis Review, the newspaper of the Roman Catholic Archdiocese of St. Louis.
These are the kinds of thorny questions that Zink thinks it's time Americans tackled on a national level. Just as President Bush's policy on stem-cell research has launched a national discussion on the issue, a movement to create a standard system could prompt more Americans to start thinking about organ donation and how donors should be enlisted.
Greisling, who is now walking, doing errands and bowling without the aid of oxygen, says he's hopeful that when people take the time to think carefully about organ donation, most will be willing to volunteer. After receiving his new lung, Greisling immediately wrote the family of the donor to thank them. He recently got a reply from the mother.
"She apologized for not writing me back sooner, but every time she sat down to write she'd cry," he said. "She said her son, Randy, was a wrestler, a popular student and a prince. She was sure this is the kind of thing he'd want to do."