How (Not) to Integrate Blood Subtyping Technology to Kidney Exchange∗

Even though kidney exchange became an important source of kidney transplants over the last decade with the introduction of market design techniques to organ transplantation, the shortage of kidneys for transplantation is greater than ever. Due to biological disadvantages, patient populations of blood types B/O are disproportionately hurt by this increasing shortage. The disadvantaged blood types are overrepresented among minorities in the US. In order to mitigate the disproportionate harm to these biologically disadvantaged groups, the UNOS reformed in 2014 the US deceased-donor kidney-allocation system, utilizing a technological advance in blood typing. The improved technology allows a certain fraction of blood type A kidneys, referred to as subtype A2 kidneys, to be transplanted to medically qualified patients of blood types B/O. The recent reform prioritizes subtype A2 deceased-donor kidneys for blood type B patients only. When restricted to the deceased-donor allocation system, this is merely a distributional reform with no adverse impact on the overall welfare of the patient population. In this paper we show that the current implementation of the reform has an unintended consequence, and it de facto extends the preferential allocation to kidney exchange as well. Ironically this “spillover” ∗Sönmez acknowledges the research support of Goldman Sachs Gives via the Dalinc Ariburnu Goldman Sachs Faculty Research Fund. Sönmez and Ünver acknowledge the research support of NSF via award SES #1426440. Yılmaz acknowledges the research support of TÜBİTAK via program 2219. †Department of Economics, Boston College, and Distinguished Research Fellow, Koç University; [email protected]; www.tayfunsonmez.net ‡Department of Economics, Boston College, and Distinguished Research Fellow, Koç University; [email protected]; www2.bc.edu/utku-unver §Department of Economics, Koç University; [email protected]; home.ku.edu.tr/ ̃ozyilmaz