Of all the organs that fail – among them the heart, lungs, and liver – treating kidney failure has produced the best results. This is due to the use of medications and dietary restrictions, but more importantly by taking over declining kidney function with dialysis and transplantation. A new study looks at the kidney availability imbalance that hinders more transplants from taking place.
Our kidneys serve many roles, to remove water-soluble toxins and metabolic products from our body, balance the amount of water within, and participate in the control of our blood pressure. We have medications to complement all of these processes, but when our kidneys fail, no amount of medicine can balance our hydration and remove toxins; for that, we need dialysis or a new kidney. Luckily for us, we have two kidneys, and we need to lose almost 85% of their function before we need to worry about medical intervention.
Dialysis uses a membrane, either artificial in the case of hemodialysis or natural (our abdominal cavity) in peritoneal dialysis, to partition excess fluid and toxins that can then be removed. While dialysis is life-saving and extending, it requires significant time every day in the case of peritoneal dialysis and three times a week for hemodialysis. The best solution for failed kidneys is transplantation, and here we have a mismatch between the supply and demand.
“More than 661,000 Americans have kidney failure. Of these, 468,000 individuals are on dialysis, and roughly 193,000 live with a functioning kidney transplant.” NIH
Of those half-million individuals (the demand), only about 20% will get a transplant. Why is the supply so low?
There are only two sources of kidneys, cadaveric, from donors who have died based upon brain death criteria and have chosen to donate their organs. Living donors, who altruistically offer up one of their kidneys – unlike blood, it is illegal to receive financial compensation to donate a kidney in the US. While there are differences in the outcome from cadaveric and living donors, they are not significant enough for anyone to turn down a kidney.
Cadaveric donations represent about 60% of transplantations. In a macabre way, the opioid epidemic has increased supply because of the concomitant increase in overdose deaths which are often due to hypoxia and allow time to retrieve and transplant kidneys. One of the first behavioral nudges was to put the option of being an organ donor on our driver’s license applications. In the UK, you are automatically a donor; you have to opt-out. In the US, the choice is often just yes or leaving the field blank. Researchers have found that forcing the question by requiring a yes or no, reduces donors.
Living donors are altruistic, and often they are donating to a friend or family member – it makes sense, few of us are willing to part with a kidney, to begin with, let alone to a stranger. Additionally, living donors must be a match to the recipient. To be fair, our abilities at immunosuppression in transplantation have advanced where being a match is not quite as tricky as it was early on. But when a donor motivated by helping a friend finds that they are not a match, they rarely continue the process. To harness that altruism and increase donors, we can thank Alvin Roth, a Nobel-winning economist.  His work was on how markets can be designed to improve allocation.
“This may sound purely theoretical, but these algorithms are great for solving real-world problems in markets where both sides have a voice, …“markets where prices don’t do all the work,” …[where] everyone wants the best possible match, but the parties usually have very different goals and priorities.” 
There are any number of these matching markets. In medicine, Dr. Roth applied his algorithms first to match graduating medical students with residency training. Both sides could rank their choices, and the algorithms provided the best outcome for both parties. This year, those algorithms filled 36,179 of 38,106 positions leaving only 3.6% unfilled.
Transplant surgeons had found a simple way to harness that living donor altruism; they created a two-donor, two-recipient match. Altruistic donor A gave their kidney to patient B, while patient B’s altruistic donor gave their kidney to patient A. Dr. Roth used the algorithms he had developed along with that initial altruistic donor to create chains of donations. Instead of these two transplant swaps, you could match far longer series. Kidney transplant chains have gotten as big as “34 kidney transplants across 26 different hospitals.”
There remains a bit of a challenge in this chain, that first altruistic donor was making a non-directed donation, not to their friend or family but a stranger – they had to trust that the algorithm and circumstances would result in the transplant for their significant other. Would it be possible to increase trust with a guarantee? A new study looked at that question. Here is what the researchers found.
The study involved 79 transplant centers, all part of our national transplantation program's Organ Procurement and Transplantation Network (OPTN). Living donors who were unable to provide a directed transplant to their friend or a family member received a voucher at the time of donation, which the donor would give to their friend or family member.
“Vouchers had no cash value and could not be sold, bartered, or transferred to another person. When a voucher was redeemed, a living donation chain was used to return a kidney to the voucher holder.”
Because there was no time limit, a donor might be prompted to act before the recipient needed a transplant, “just in case” their renal insufficiency became failure.
- Between 2014 and 2021, there were 250 “family vouchers” issued.
- Each kidney resulted in more than one transplant, 573 overall.
- Of the vouchers, six were redeemed a month to five months after the donation.
- Of those six, three were in blood type O recipients. While O blood is the universal donor, only blood type 0 matches type O recipients. (AB in the universal recipient)
The evidence from this admittedly small study is that
“…the family voucher program appeared to mitigate a major disincentive to living kidney donation, namely the reluctance to donate a kidney in the present that could be redeemed in the future if needed.”
As the editorial accompanying the study points out, the mismatch between supply and demand in kidney transplantation has real consequences. Patients die while waiting, 89,000 in the last twenty years, or become too ill to be considered a transplant candidate (roughly another 54,000). This voucher program involves donating today with the promise of receiving tomorrow – an arbitrage of time, not finances. This seems like an incentive that has no ethical objections. There is no “cutting the line.” It is a program we should expand.
 Actually, he did not receive a Nobel – there is no Nobel in economics; it is the Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel, something you can use in a trivia contest.
 Matching Kidney Donors with Those Who Need Them—and Other Explorations in Economics National Academy of Sciences
Sources: Voucher-Based Kidney Donation and Redemption for Future Transplant JAMA Surgery DOI: 10.1001/jamasurg.2021.2375
A Regulated System of Incentives for Kidney Donation—Time for a Trial! JAMA Surgery DOI:10.1001/jamasurg.2021.1435
For more on Alvin Roth, consider this episode of Freakonomics, Make Me a Match (Ep. 209)