Paired Kidney Exchange

Reported October, 2007

Pittsburgh, Penn. -- More than 70,000 Americans need a kidney transplant. Four-thousand will die this year waiting for a suitable organ to become available. But a revolutionary computer software program is matching live donors with those in need.

For the Repasky family, a healthy meal is one that's low in sodium. Marnie and Hal's sons have kidney disease.

"My oldest son has had two kidney transplants. My youngest son has had two transplants. We fully understand the need for organs and organ donation," mother Marnie Repasky says.

19 year-old Nathan received his second kidney last year from his sister-in-law, Susan. The Repasky's are fortunate. Many times, patients and loved ones willing to donate have blood or tissue types that don't match. When that happens, the incompatible donor and patient may agree to try paired kidney donation: donor A would give a kidney to patient B, while donor B would give a kidney to patient A. Transplant experts say paired donation is successful, but is often difficult to coordinate.

That's where computer scientist Tuomas Sandholm, Ph.D., from Carnegie Mellon University in Pittsburgh, Penn., makes a difference. Dr. Sandholm designed computer software that finds multiple matches.

"It's a very complex problem of deciding what kidney goes to whom," Dr. Sandholm says.

Algorithms already exist for two-way paired donation, but Dr. Sandholm's program keeps doing the math. It calculates the most efficient way to exchange the kidneys, resulting in multiple possible combinations. For example, donor A would donate to patient B, donor B would give a kidney to patient C, donor C would go to patient D, and so on -- up to four or five-way swaps, where the last donor would give an organ to patient A.

Sandholm's algorithm is already being used successfully -- last December, a network of 55 transplant centers began using the software.

"This really is the enabling technology to get a nationwide kidney exchange going."

For the thousands of families affected by kidney disease, it's welcome news.

"Time is such a precious commodity to everybody. But to somebody who needs a transplant, it's even more so," says kidney recipient Nathan Repasky.

Sandholm's algorithm can analyze 10,000 donor and patient pairs. He said existing algorithms were only able to handle data from 900 pairs.

The American Mathematical Society and the Mathematical Association of America contributed to the information contained in the TV portion of this report.

Click here to Go Inside This Science or contact:

Tuomas Sandholm
Carnegie Mellon University
Pittsburgh, PA 15213
(412) 268-8216
sandholm@cs.cmu.edu

American Mathematical Society
Providence, RI 02904-2294
(800) 321-4267
http://www.ams.org

Mathematical Association of America
Washington, DC 20036-1358
(800) 741-9415
http://www.maa.org

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