A Matching Algorithm for Paired Living Kidney Donation in the UK

1. A Matching Algorithm for Paired Living Kidney Donation in the UK Joanne Allen – Senior Statistician NHS Blood and Transplant

2. Background

3. X X Paired living kidney donation Blood group and tissue type incompatibility prevent many potential living donor kidney transplants A simple exchange of suitable donor kidneys is one possible solution ‘Couple’ 1 ‘Couple’ 2 Recipient 1 Recipient 2 Donor 1 Donor 2 Human Tissue Act made this possible in the UK from Sept 2006

4. Background • The British Transplantation Society and NHS Blood and Transplant worked together to develop arrangements for paired donation in the UK – working party • Diverse range of views • A national scheme • is required by the HTA • will maximise the potential of paired donation - although a ‘local’ bias is preferred • will be regularly reviewed • should be limited to paired rather than pooled donation initially

5. Stages involved in the UK paired donation scheme

6. 1 2 5 3 4 Matching process Stage 1: Identify all possible 2-way exchanges Say we have 5 couples and couple 1 can swap with any other and couple 4 can swap with couples 3 & 5 Each circle represents one incompatible donor-recipient couple

7. 1 2 5 3 4 Matching process Stage 2: Determine all combinations of exchanges

8. Matching process Stage 2: Determine all combinations of exchanges 1 1 2 2 5 5 3 3 4 4

9. Matching process Stage 2: Determine all combinations of exchanges 1 1 2 2 5 5 1 3 3 4 4 2 5 3 4

10. Matching process Stage 2: Determine all combinations of exchanges 1 1 2 2 5 5 1 3 3 4 4 2 5 1 3 4 2 5 3 4

11. Matching process Stage 2: Determine all combinations of exchanges 1 1 2 2 5 5 1 3 3 4 4 2 5 1 1 3 4 2 2 5 5 3 3 4 4

12. Matching process Stage 3: Optimum combination 1 1 X 2 2 5 5 1 X X 3 3 4 4 2 5 1 1 X X X 3 4 2 2 5 5 X 3 3 4 4

13. Matching process Stage 3: Optimum combination 1 X 2 5 1 X 3 4 2 5 3 4

14. Prioritisation factors To determine who is transplanted and who donates to whom Blood group match Local exchange Sensitisation Tissue type match Age difference between the 2 donors

15. Simulations

16. Simulations • Having identified relevant factors, simulations were written in SAS and were used to inform decision-making on • effective waiting list sizes • appropriate weights for prioritisation factors • likely chance of transplant for different types of patient • Simulations based on real data from 20 centres • 400 transplants that could not proceed over 2-year period due to blood group and/or tissue type incompatibility

17. Simulations • The SAS simulation program: • selects a stratified random sample, ensuring an even mix of blood group and tissue type incompatible couples • Identifies all possible two-way exchanges, ensuring that the donors and recipients are blood group and tissue type compatible in both sides of the exchange • Determines the priority score for each of the two-way exchanges, based on weights specific to each simulation • Determines all combinations of exchanges (or a subset of combinations when dealing with large pool sizes) • Determines the optimum combination of exchanges (highest overall priority score), ensuring that each donor and recipient is not involved in more than one exchange • 10 simulations for each scoring system and pool size

18. How many couples are needed? Maximum % transplanted 10 simulations were run for each pool size, using a stratified random sample No. of couples on list

19. Prioritisation factors • How many points for • Local exchange (based on 5 areas of the UK) • HLA match (4 levels) • Sensitisation (% of blood group identical donors having antigens which are declared unacceptable for the recipient – pool of 10,000) • Age difference between the 2 donors • Blood group match – consider restricting use of O donors • Identify combination of transplants with highest sum of point scores for individual transplants

20. Proposed scheme - results * Based on single factor scoring

21. Proposed scheme - results * Based on single factor scoring

22. Proposed scheme - results * Based on single factor scoring

23. Proposed scheme - results * Based on single factor scoring

24. Proposed scheme - results * Based on single factor scoring

25. Agreed national matching scheme • Points for each possible transplant in a combination - • Local exchange: 20 points • Sensitised patient: 0-50 points for 0-100% sensitised • HLA matched transplant: 0–15 points for levels 4 to 1, respectively • Small donor-donor age difference: 3 points if <=20 years • Also - restrict use of group O donors to group O recipients only • The highest scoring combination is identified • The maximum possible number of transplants will be achieved • Note – at registration, HLA match and donor age requirements can be specified

26. Who is most likely to find a match? Based on 200 simulations of 30 couples, average transplant rates in the first matching run are - 23% blood group incompatible 34% HLA incompatible Among HLA incompatibles

27. Who is most likely to find a match? Blood group incompatible Tissue type incompatible

28. Where are we now?

29. Matching run summary

30. Matching run summary

31. Matching run summary

32. Matching run summary

33. Matching run summary 3-way exchanges considered in April 2008 run onwards, following agreement from the Kidney Advisory Group

34. Donor 1 Donor 2 Donor 3 Donor 4 Donor 5 Recip 1 Recip 2 Recip 3 Recip 4 Recip 5 Pooled donation 2-way exchange 3-way exchange

35. Matching run summary

36. Matching run summary

37. Matching run summary * Transplants did not proceed for various reasons

38. Blood group composition of October 2008 list Many more A donors than A, AB recipients

39. Degree of sensitisation for patients on October 2008 list

40. Altruistic donor Pooled donor ‘couple’ - 1 Pooled donor ‘couple’ - 2 Patient on deceased donor transplant list Future development Domino paired/pooled donation

41. www.uktransplant.org.uk joanne.allen@nhsbt.nhs.uk

42. Thank You