Until the mid-1990s, kidney transplants from live donors who were not genetically related to the recipient were rare. As mentioned in a May 2010 blog post, most hospitals had a policy of rejecting donation offers from spouses or other unrelated people. The thought was that the risk of any live donor surgery was too great unless the benefit of a better HLA match outweighed it. This meant the only allowed sources of transplant kidneys were close relatives and deceased donors.

Policies at hospitals changed as 1) the advantage to recipients of receiving a kidney from a relative fell with improvements in immunosuppressant medications, 2) the risk to donors of surgery declined with the development of laparoscopic techniques, and 3) public attitudes about donor informed consent began to favor the belief that unrelated donors were making their offer for altruistic reasons rather than selfish ones (like being compensated or ego gratification or coercion).

The figure below shows the number of kidney transplants performed each year in the U.S. from 1998 to 2009. As mentioned in an Apr 2010 blog post, the rise in transplants mirrors the rise in the incidence of end-stage renal disease in the U.S. The proportion of transplants from live donors rose from under 20% in 1988 to a peak of almost 43% in 2003. It then dipped for a few years and is rising once again.


All transplants. Data from UNOS

Looking at the figure below, the composition of the live donors has been changing dramatically. In 1988, only 71 kidneys were transplanted from unrelated donors (the New York Times article reports a lower number) representing 4% of living donors. The proportion of unrelated donors has been steadily rising and now accounts for about 43% of all living donations. Notice that after a quick rise, the number of donations by spouses or life partners has leveled off. The most common sources of unrelated donors now are friends, neighbors, coworkers, church members, and even strangers that meet on the Internet.


Live donor transplants. Data from UNOS

Even more interesting is the extremely rapid rise of alternative sources of living donors. The last three lines from the figure above are rescaled in the figure below. The fastest growing source of living donors is paired exchanges. As described in a Mar 2010 blog post, a kidney exchange involves the trade of kidneys between two sets of incompatible pairs. Each pair consists of a recipient and a willing, medically suitable donor who is either blood type or HLA incompatible. Through an exchange, they can find another pair in the same situation but where the donors match the recipients in the other pair. Kidney exchanges have the potential of becoming the leading source of live donor kidneys within a few years. (More about that and the potential of adding compatible pairs to exchanges in a future blog post.)


Exchanges and anonymous transplants. Data from UNOS

A living/deceased exchange is similar to a paired exchange, except that the recipient in the pair receives a kidney from a deceased donor rather than from a live one. Under UNOS rules, people who have donated organs receive 4 points if they ever need to enter the transplant waiting list. This is often enough to move them to the top of the list. In a living/deceased exchange, the donor provides her organ to a patient on the UNOS list and provides her 4 points to her incompatible recipient. The recipient is now at or near the top of the list to receive an organ from a deceased donor.

Since receiving a kidney from a live donor generally produces superior medical outcomes to one from a deceased donor, a living/deceased exchange does not produce the best possible outcome for the recipient participating in the exchange. Yet despite the growing use of paired exchanges, the number of patients participating in living/deceased exchanges is also growing. Hopefully, paired exchanges will grow fast enough to soon make living/deceased exchanges unnecessary. (Incidentally, the process for managing living/deceased exchanges is covered under a patent application. My low opinion of business process software claims can be seen in this Mar 2010 blog post.)

The final fast-growing source of donors are people who donate without a specific recipient in mind. They are called nondirected or altruistic donors. Johns Hopkins Medicine claims to have performed the first nondirected live donor transplant in September, 1999 (though UNOS data shows five other nondirected donors in 1999, three in 1998 and one in 1988, the first year data is available).

In addition to increasing the total number of donations, nondirected donors also play an important role in starting donor chains in kidney exchanges. Donor chains reduce the risk to recipients of their matched donors backing out an exchange after the first transplant takes place. Thus, nondirected donors reduce the need to perform the transplant surgeries simultaneously. This simplifies scheduling personnel and operating rooms for kidney exchange transplants.

To learn more about becoming a nondirected donor in a kidney exchange, contact a transplant center and ask if it participates. Lists of some participating centers are available at the National Kidney Registry, Alliance for Paired Donation, Paired Donation Network, and New England Program for Kidney Exchange.

[Update: This data is examined at the transplant center level in a Jul 2010 blog post.]