For some people, the more they know about the process makes them less inclined to follow through with donation.
"Drilling holes in bone, being on narcotics, being in pain, dealing with bruising, etc., may interfere with what you may be doing or valuing," said Cronin.
"Morally, others are relying on you to carry through on your promise," said Arthur Caplan, director of the Center for Bioethics at the University of Pennsylvania. "But legally, you have the right to say no at any time."
Caplan said the legal framework is the belief that a person's choice overrides the needs of others, and referenced a court case from the 1970s that helped set precedent.
"A cousin agreed to donate bone marrow to his cousin and backed out, but the court refused to compel or force any donation," he said.
But despite the legal protections, Caplan said, people need to consider their decision to register as a donor very carefully.
"If a potential donor is bailing out, they need to understand they may be the sole source for that person and it may have a terrible impact. There may not be time to find a suitable donor."
"Once a match is found, it's like hitting the lottery, but now it depends on full consent to the procedure, and it must be devastating if a person backs out," said Cronin.
Cronin said there may also be psychological consequences for the donor as well as the intended recipient.
"If they understand the consequences of not donating, they may have significant guilt or depression."
"The registry has a moral responsibility to push, advocate and make the case for a donation, but can't force it," said Caplan.
"As a donor center, we also represent the donors," said Harf. "We have an obligation to donors not to make them feel bad if they change their minds."
Harf and Abress, both vice presidents at bone marrow centers, say they try to prevent changes of heart for financial reasons as well. It can cost between $65 and $100 to register a person.
"We could invest that money in people who will come through," said Harf.
They try to encourage people to honor their commitments by stressing donor education and communication.
"We urge people to sign up, but before they do, they need to educate themselves about the process," said Harf. "If, in the beginning, they have any doubt, we make sure we let them know it's okay if they don't sign up. We turn away people if we think they're not sure."
"We're contacting donors earlier in the process based on the resulting match list so we can know their interest and get their health information so by the time transplant centers make a selection, we know they're going to go forward with it," said Abress.
Both centers encourage potential donors to keep their information updated and consider their decision earlier rather than later.
"We would rather have donors change their participation status at a time when they're not active in a patient's search," said Abress.
And if Brian Lindenberg has his way, people wouldn't change their minds about bone marrow transplants at all.
"We're trying to ... [get] the word out how important it is not only to get on the registry, but how simple it is to be a donor and how important it is to go through if you get that call," he said.