One of the latest innovations in helping patients with end-stage renal disease (ESRD) find live donors is the kidney swap. A kidney swap starts with a kidney patient who knows a person willing to donate but is not tissue compatible (let’s call them pair 0). If that patient finds another pair in a similar situation (let’s call them pair 1), then there is a chance the two pairs may be able to swap donors to produce a compatible match. If this happens both patients get a transplant and both donors can provide the gift of life, though not to their originally intended recipient (see image below).


An example kidney swap. Graphic by George Taniwaki

It is generally too difficult for patients to find partners for a kidney swap on their own (for a rare counterexample see Globe and Mail Feb 2011). Thus, these swaps are usually facilitated by the hospital where the patients are registered on the transplant waiting list. A transplant nephrologist at that hospital will periodically scan the list of patients with unmatched donors (done by computer nowadays) and see if any pairs potentially match. If any do, a transplant surgeon will review the matches to approve/reject the surgeries, a blood lab will run cross-match tests to ensure the patients’ immune systems will not react to the potential donors’ organs, and a transplant coordinator will schedule the surgeries.

These kidney swaps are a growing source of kidney transplants and now account for over 300 transplants a year in the U.S. (for more details on the rise in kidney swaps, see this Jun 2010 blog post).

However, unless the hospital had a large pool of unmatched pairs (say over 20 pairs), it would be unlikely to find matches for its sensitized patients who require more closely matched kidneys. To find matches for these patients, it needs a bigger pool to choose from. Thus, smaller hospitals began to band together to form kidney exchanges. There are now several such exchanges in the U.S., each vying to become the largest in order to maximize the chance of finding a match and thus minimizing the wait time for participating patients.

Natural monopoly

If size of pool was the only factor that led to more transplants getting done faster, then the exchange with the largest pool, even if it was only slightly larger than the others, would provide more matches and do them faster. Hospitals that were members of other exchanges (or doing swaps in-house), would see the success at this exchange and would switch to it, making the pool even larger, leading to even more matches faster. Eventually, all hospitals would join this one exchange to take advantage of the gains in performance and all the other ones (including the in-house exchanges) would be driven out of the market.

However, we don’t see this. For instance, an article in SFGate  Apr 2011 highlights a 5-way swap that California Pacific Medical Center just completed, its largest single-swap ever. Yet California Pacific also is a member of the largest kidney exchange in the U.S.


A five-way swap. Graphic from SFGate

In a similar vein, I recently attended a seminar held by one of the transplant centers in Seattle. The director of kidney transplant program stated that the center had performed several swaps in the past year, all in-house. They were also working with all the other transplant centers in the northwestern U.S. (4 in Seattle, 1 in Spokane, and 3 in Portland) to form a regional exchange. This would be in addition to the in-house exchanges and national exchanges that all these transplant centers participate in.

These stories highlight the growing interest in kidney exchanges among transplant centers. But they also point to a failure by the national kidney exchanges to meet the needs of their member hospitals.

I believe there are three reasons we see this reluctance by transplant centers to rely on large national kidney exchanges for all their swaps. They are the fear in missing some  transplants, fear of loss of efficiency and control, and fear of medical risks. I will describe each of these in the next blog entry.