Nov. 12, 2010 -- Brian Lindenberg of Ridge, N.Y. is coping with the pain of losing his 37-year-old wife, Penny, to leukemia last month.

But he's also coping with the pain of believing her death may have been prevented if only potential bone marrow donors didn't change their minds.

"It was terrible in the end, knowing that help was out there. This didn't have to happen. Someone didn't do their part and follow through," Lindenberg said in an interview with WABC-TV.

He said they were ecstatic when they first got the news that there was a bone marrow match. It happened four different times -- but each time, their hopes were dashed when anonymous donors backed out on offering their marrow for transplant.

"To walk away? To close the door and forget about it?" family friend Chris Herrick said.

As tragic as Penny Lindenberg's story is, those who are closely involved with bone marrow transplants say many potential donors eventually change their minds about it.

"The national average is that 47 percent of people on donor registries say no when they are asked to donate," said Katharina Harf, executive vice president in the U.S. of the German-based bone marrow organization DKMS.

"Many times, people sign up based on emotional appeal, and it turns out to be a lot for people, and then they don't want to do it," said Dr. David Cronin, associate professor and director of adult and pediatric liver transplantation at the Medical College of Wisconsin.

There are many reasons people may decide against donation after they register.

"One reason is their health changes and donating could be detrimental to them or to the recipient," said Linda Abress, vice president of donor and cord blood management services at the National Marrow Donor Program. "Another reason is they are temporarily unavailable – it could be a short-term illness, pregnancy or certain life circumstances that make them unable to go through the process."

Abress said other people move and can't be located. Or they may simply just decide they're no longer interested in donating.

Many people do not know what's involved in the donation process.

"There's a big misconception that bone marrow donation is painful," Harf said. "One of the other big misconceptions is that the cells are collected from the spine."

The early stages of the process include swabbing the inside of the cheek to check for HLA (human leukocyte antigen) type, which is an indicator of compatibility. Potential donors also must go for a complete physical and blood test. They also must sign multiple consent forms at different stages of the process.

People can donate bone marrow in two different ways. One is by undergoing a procedure similar to donating plasma. The donor gets an injection of a drug to increase the number of blood-forming cells and then donates blood. The marrow cells are then separated from the blood.

The other method of collecting bone marrow is an outpatient surgical procedure that involves inserting a needle into the pelvic bones and extracting marrow cells.

While there may be some physical side effects from both procedures, experts say they disappear in a matter of days.

Donors Have a Moral Obligation, But Not a Legal One

There may also be psychological side effects as well.

"Donors want to do the right thing. If the recipient has a bad outcome, they may feel guilty," said Cronin. "The closer the relationship, I would imagine the psychological impact would be greater."

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."

Donor Centers Stuck in the Middle

"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.

For more information or to register as a donor, go to www.getswabbed.org or to bethematch.org.