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Organ Donation and Matching Markets

Due to the complicated nature of medical transplants and the human body, the organ matching process is a much more complicated example of matching markets than we are able to cover in class. Factors such as blood type, body size, medical condition, and patient-donor distance all play a role in determining how the matching occurs. To make matters even more complicated, there are certain rules and limitations each organ faces. For example, people awaiting heart transplants are also assigned a code that indicates how urgently they need one. The heart can live outside the body for 4-6 hours, so time is an issue and we must also factor in how far the recipient lives from the donor, gradually increasing the search distance until a match is found. The size of the donor heart vs. the body of the patient is also important, since the heart must fit inside the recipient’s ribcage.

A few years ago, an algorithm developed at Carnegie Mellon that matches kidney donors with compatible recipients was used in a push to increase the number of kidney paired-donation transplants. The number of recipients waiting far exceeds the number of donors, and things like increasing the size of the search network can help increase the number of matches. Some challenges when designing such an algorithm include time and space efficiency. Due to the number of people in the system, the algorithm needs to be designed cleverly so as to finish within a reasonable amount of time. Also, limited memory is an issue so they needed to store into memory only things that are pertinent to current calculations.

Some things to ponder while thinking about organ donation systems include what happens in terms of updates? That is, are people waiting for a donation monitored and placed higher on the list if their condition worsens? Another point of consideration is how two equal people are treated – if two people have the same blood type, body size, location, urgency, etc., what determines who is placed higher on the list? I would imagine a situation like this being fairly frequent in densely populated areas such as New York City. In real-world applications, fairness is important, especially to those waiting for a donor. Also, in class we covered a kidney donation matching situation in which a patient has a willing donor but they are incompatible (initial endowments). I think it would be interesting to design a system where the patient needs one organ but his initial endowment donor is looking to provide a different one.



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