Compatible pairs in kidney exchange

The question of whether compatible patient-donor pairs should be invited to take part in kidney exchange is gaining some exposure with recent articles and news items in the medical literature. The issue is that if kidney exchange is restricted to patients who are incompatible with their live donors, we will be seeing many fewer blood type O donors than are in the general population, so exchanges will be more difficult to find, and there will be fewer transplants than if there weren't such a shortage. (Since O donors don't have a blood type incompatibility with any recipient, most of them will be compatible with their intended recipients; O donors are only incompatible if there is some other, immunological incompatibility.)

Here's a story from the most recent, Feb 2010 Nephrology Times: Dramatic Increase in Transplant Rates Projected if Compatible Pairs Are Included in Kidney Swaps

It follows up on a recent article by Lloyd Ratner, of Columbia University/New York–Presbyterian Hospital, reporting such a three-way exchange (Transplantation, 2010;89:15-22). The story also interviews some of the other pioneering surgeons involved in kidney exchange, including Frank Delmonico, Bob Montgomery and Steve Woodle.

Inviting compatible pairs to participate in exchanges seems like a very good idea indeed. (An early discussion, with simulations to provide quantitative estimates of the effect of including compatible pairs (which is quite large), was reported in Table 1 of:
Roth, Alvin E., Tayfun Sonmez, and M. Utku Unver, "A Kidney Exchange Clearinghouse in New England" American Economic Review, Papers and Proceedings, 95,2, May, 2005, 376-380. )