Phil Fischer's wife likes to joke that at least her husband's kidney gets to go out dancing every once in a while.

About two years ago, Fischer joined the small but growing number of people who've donated a kidney to a stranger in need.

The organ went to a woman whom Fischer has never met but later learned about from a letter that didn't reveal her identity. Evidently, she enjoys spending time with her grandchildren, golfing and dancing.

“I think it did something good for somebody else in the world,” said Fischer, 58, a pediatrician at the Mayo Clinic in Rochester, Minn. Of his motivation, he simply said: “It was something I was supposed to do, so I did it.”

For a period dating back to 2000, transplant centers across the United States saw a steady increase in the number of live donors such as Fischer who were willing to give a kidney to a stranger. By 2010, the annual tally underwent a tenfold increase to just over 200 kidneys.

Along the way, the donations generated good publicity for proponents of kidney donation, since a so-called nondirected donor can help kick off a chain of transplant surgeries that effectively stretch the supply of kidneys while helping recipients who'd otherwise get sicker while languishing on the waiting list.

But since 2010, annual tallies have dropped back to about 150 in the midst of a broad decline in the number of donors willing to give a kidney to a friend or relative. Doctors say they are at a loss to explain the broader slowdown and suggest that raising awareness is one of the only ways to rekindle growth in nondirected kidney donations.

“Every year, the number of people on the waiting list grows, so the average waiting time between being listed and receiving a deceased donor transplant continues to increase,” wrote Dr. Arthur Matas, a transplant surgeon at the University of Minnesota, in an email. “In the 1980s, I would tell a new patient it would be about a year till they had a deceased donor kidney. Now, I tell them 5-6 years.”

Nearly 99,000 people in the United States are waiting for a kidney transplant. Through the first eight months of this year, just over 11,000 kidneys were donated, with about two-thirds coming from deceased donors.

The remaining 3,771 kidneys donated this year came from living donors, including 106 from people who didn't direct their kidneys to a particular recipient.

In the late 1990s, the University of Minnesota became one of the nation's first medical centers to transplant kidneys from donors of nondirected organs. As of August, 80 such donors have been treated at the University of Minnesota Medical Center, Fairview — the highest tally for any one hospital in the country, according to figures from the United Network for Organ Sharing.

Over the years, nondirected donors have provided kidneys at Abbott Northwestern Hospital in Minneapolis, Hennepin County Medical Center and the Mayo Clinic, as well. Across all four Minnesota hospitals, donors collectively have provided 114 nondirected kidneys, about 8 percent of the national total.

“We were the first center to do this and report on it,” Matas wrote. “Potential donors, after hearing we would do this, came from all over the country. As more centers started doing this, our donors (now) are mostly local.”

In 2010, a nondirected kidney donor helped kick off an unusual series of five kidney transplant surgeries, with donors and recipients being operated on at the U, Abbott Northwestern and Sanford Health Medical Center in Fargo, N.D.. The surgeries are known as a “kidney chain,” and the nondirected donor plays a key role in such operations.

In a chain, the nondirected donor's kidney goes to a recipient who has a friend or relative who's willing to donate but can't give to their loved one because of a physical incompatibility. So, the incompatible donor gives a kidney to a different recipient, who also has an incompatible donor.

The chain continues in this “pay-it-forward” fashion for as many surgeries as hospital officials can coordinate. The donors and recipients are part of what's called a “paired kidney exchange program,” and the chain ends when a recipient's donor can't give to another incompatible recipient/donor pair. That donor winds up giving to the next patient on the hospital's waiting list.

“Our center has done 15 paired exchanges so far, and 10 of them have been as a result of a nondirected donor starting that chain,” said Margaret Voges, a nurse and transplant coordinator at the U.

There also are chains that, in a sense, never end, Voges said. The last donor in the lineup doesn't give a kidney back to a hospital's waiting list but instead waits until another incompatible recipient/donor pair can be found. The donor in such a situation “bridges” over time, so the chain eventually continues.

Currently, the U is in the middle of two such chains, Voges said. Chains help expand the supply of donor kidneys and also help patients get a donor kidney sooner.

“Last year, we were able to prevent a patient having to go on kidney dialysis because of a chain involving a bridge donor,” she said.

Mayo Clinic has coordinated at least eight or nine kidney chains started by nondirected donors, said Dr. Mikel Prieto, surgical director of the kidney and pancreas transplant program for the clinic in Rochester. The chains help highlight the impact of nondirected donors, but hospitals remain cautious about promoting the nondirected option.

Donors have a minimally invasive surgery that typically involves two days in the hospital and a few days of post-operative pain. Recovery takes several weeks, although donors in the long run don't have an increased risk of health problems.

When Mayo Clinic performed its first kidney transplant with a nondirected donor about 10 years ago, there was reluctance about the idea, Prieto said, because doctors questioned why donors would give up a kidney.

“We've realized these are just people with a strong sense of altruism,” he said. “We are thinking of making (this option) a little more visible, so people know about it if they are so inclined. But we haven't been too aggressive.”

Matas of the U said in an email: “If donation were risk-free ... we would advertise. But there is no getting around the fact that although the risk is small (risk of death related to the surgery is about 3/10,000), it is still a risk.”

People thinking about becoming nondirected donors should consider the risks as well as the time involved, said Fischer, the Mayo Clinic physician who donated two years ago.

Before they're cleared to give a kidney, donors go through an extensive evaluation of their physical health, as well as their motivations. Doctors want to make sure that people are giving for truly altruistic reasons — not because they're expecting something in return or are trying to deal with guilt from another situation, Prieto said.

Fischer said he was surprised by how long it took him to recover physically from the donation surgery. Even so, he has no regrets and said he won't be surprised if two of his adult children eventually become donors.

Some people give kidneys to strangers because they've seen how a kidney transplant benefits someone they know, Prieto said. Others are routinely engaged in altruistic endeavors — everything from blood donation to religious missions — and don't see kidney donation as extraordinary, he said.

“I don't think we understand the degree of commitment to altruism that some people have,” Prieto said. “They just want to do good — it's as simple as that.”

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