Other people are turned down because they are not "tissue matches," meaning for one reason or another their immune system has built up too many antibodies that will cause rejection in a later transplant.
"It's hard to get a good number of the people who are willing but don't match, because some people already know that they're obese, or that they have the wrong blood type and don't come forward," Malinzak said
At the moment, the majority of families without a match must wait on the national kidney transplant waiting list for a diseased kidney donor. As Hargis knows, the time on dialysis can be grueling and dangerous. Last year, 4,505 people died on traditional lists waiting for a kidney, according to the United Network for Organ Sharing.
"Mom was on dialysis for three to four hours a day, three days a week. My poor dad, he worked second shift so he was coming home and sleeping one to two hours and taking my mom to dialysis," Hargis said. "I'm glad he'll be getting some sleep now."
Dr. Robert Montgomery, director of the Transplant Center at Johns Hopkins Hospital, said the wait for a kidney has only gotten longer as the number of people suffering renal failure from high blood pressure or diabetes grows.
"There hasn't been much increase in the willingness of people to donate their organs after they die -- that's been a flat line -- and at the same time there's been an exponential increase in the need for kidneys," Montgomery said.
The idea of kidney swaps has circulated for decades as a way to decrease this wait, but in 2004, Montgomery said, doctors at Johns Hopkins published an article outlining the idea of the extended kidney donor chain.
"Right about 2000-2001 started to get these people calling our transplant centers saying 'I'm healthy, I have two kidneys, I only need one, I don't know anyone who needs one and I'm willing to donate,'" Montgomery said.
Then specialists at Johns Hopkins had the idea to start a chain with these altruistic living donors.
"The chain is always initiated by a donor who doesn't have a recipient," Montgomery said. "Then at the end of the chain we have a left-over kidney."
That left-over kidney "closes the chain" and goes to someone on the national waiting list who doesn't have willing donor to continue the line.
While doctors can increase the odds of getting people kidneys by including more links in the chain, the extended surgeries can come with complications -- the logistics of booking multiple operation theatres for surgeries, flights with kidneys that have a 24-36 hour time limit once they're out of the body, and overcoming unforeseen snags.
"What can happen in these paired donations is if one person along the way backs out, or gets sick and can't undergo transplant, then the whole chain needs to be reorganized," Malinzak said.
To increase the odds and decrease the complications, the United Network for Organ Sharing (UNOS) has teamed up with Johns Hopkins to develop a national registry for living kidney donation swaps.
"The more pairs you have in the system, the more likely you are to get a match, and that's why we need a national system," said Elizabeth Sleeman, a policy analyst and liaison to the kidney pair donation workgroup at UNOS.
Sleeman said UNOS is limiting the swaps to two- or three-way matches when the database launches in 2010. Montgomery estimates the potential for kidney transplants with the new database could save many lives.
"If we were able to have all the patients in the country who have incompatible donors enter into a pool, then we could do an additional 1,500 transplants a year," Montgomery said. "That is a 25 percent increase over what we currently do."