The Problem
NHS Blood and Transplant (NHSBT) estimates that over 37,500 people
in the UK have end-stage renal failure; nearly 21,000 are on dialysis.
As of 31 March 2017, there were 5,233 patients on the transplant list
for a donor kidney. The number of kidney transplants carried out each
year is much lower than this: 3,347 transplants took place between 1
April 2016 and 31 March 2017, of which 1,009 were from living donors.
There are legal frameworks to help boost the number of donors in
circumstances where next of kin is not compatible with the patient.
Under the paired kidney exchange (PKE), two or more kidney
patients can swap their willing but incompatible donors in a cyclical
fashion so that both receives a compatible kidney. Groups of three
patients in a PKE are known as three-way exchanges.
There are significant logistical challenges to carrying out PKE
transplants, partly because all operations must be performed
simultaneously to avoid the risk of donors reneging on their commitments
once their loved-one has received a kidney. Donor illness is another
risk, and the larger the number of participants, the more complex the
situation. Even three-way exchanges require significant coordination to
secure six operating theatres and surgical teams on a single day.
An early algorithm could only manage datasets of up to 100 potential
transplants, so a more capable algorithm was required to more
intelligently identify and optimise the process of PKEs.