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A Matching Algorithm for Paired Living Kidney Donation in the UK

This study explores a matching algorithm for maximizing paired kidney donations by identifying exchanges and prioritizing factors such as blood group compatibility and sensitization levels. Simulation-based decision-making aids in determining the best transplant combinations. The proposed scheme, with factors like HLA matching and age difference, aims to achieve the highest number of successful transplants. The agreed national matching scheme allocates points to each transplant scenario for efficient pairing. The study's findings highlight the likelihood of finding a match among blood group and HLA-incompatible donors and recipients.

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A Matching Algorithm for Paired Living Kidney Donation in the UK

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  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

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