RSS Avon Local Group, 14 October 2008 A Matching Algorithm for Paired Living Kidney Donation in the...
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Transcript of RSS Avon Local Group, 14 October 2008 A Matching Algorithm for Paired Living Kidney Donation in the...
RSS Avon Local Group, 14 October 2008
A Matching Algorithm for
Paired Living Kidney Donation in the UK
Joanne Allen – Senior Statistician
NHS Blood and Transplant
RSS Avon Local Group, 14 October 2008
Background
RSS Avon Local Group, 14 October 2008
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
Paired living kidney donation
XX
Human Tissue Act made this possible in the UK from Sept 2006
RSS Avon Local Group, 14 October 2008
• 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
Background
RSS Avon Local Group, 14 October 2008
Stages involved in the UK paired donation scheme
RSS Avon Local Group, 14 October 2008
1
2
34
5
Say we have 5 couples and couple 1 can swap with any other and couple 4 can swap with couples 3 & 5
Matching processStage 1: Identify all possible 2-way exchanges
Each circle represents one incompatible donor-recipient couple
RSS Avon Local Group, 14 October 2008
1
2
34
5
Matching processStage 2: Determine all combinations of
exchanges
RSS Avon Local Group, 14 October 2008
1
2
34
5
1
2
34
5
Matching processStage 2: Determine all combinations of
exchanges
RSS Avon Local Group, 14 October 2008
1
2
34
5
1
2
34
5
1
2
34
5
Matching processStage 2: Determine all combinations of
exchanges
RSS Avon Local Group, 14 October 2008
1
2
34
5
1
2
34
5
1
2
34
5
1
2
34
5
Matching processStage 2: Determine all combinations of
exchanges
RSS Avon Local Group, 14 October 2008
1
2
34
5
1
2
34
5
1
2
34
5
1
2
34
5
1
2
34
5
Matching processStage 2: Determine all combinations of
exchanges
RSS Avon Local Group, 14 October 2008
1
2
34
5
1
2
34
5
1
2
34
5
1
2
34
5
1
2
34
5
XX
XX
X X
X
Matching processStage 3: Optimum combination
RSS Avon Local Group, 14 October 2008
1
2
34
5
1
2
34
5 X
X
Matching processStage 3: Optimum combination
RSS Avon Local Group, 14 October 2008
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
Prioritisation factors
RSS Avon Local Group, 14 October 2008
Simulations
RSS Avon Local Group, 14 October 2008
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
Simulations
RSS Avon Local Group, 14 October 2008
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
Simulations
RSS Avon Local Group, 14 October 2008
How many couples are needed?
No. of couples on list
Max
imum
% t
rans
plan
ted
10 simulations were run for each pool size, using a stratified random sample
RSS Avon Local Group, 14 October 2008
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
Prioritisation factors
RSS Avon Local Group, 14 October 2008
Proposed scheme - results
Factor Maximum possible
% of transplants*
Proposed scheme –
% of transplants
Local exchange
Sensitised patients (65-100%)
Level 1-3 HLA mm
Donor-donor age diff <= 20 yrs
* Based on single factor scoring
RSS Avon Local Group, 14 October 2008
Factor Maximum possible
% of transplants*
Proposed scheme –
% of transplants
Local exchange 51 47
Sensitised patients (65-100%)
Level 1-3 HLA mm
Donor-donor age diff <= 20 yrs
* Based on single factor scoring
Proposed scheme - results
RSS Avon Local Group, 14 October 2008
Factor Maximum possible
% of transplants*
Proposed scheme –
% of transplants
Local exchange 51 47
Sensitised patients (65-100%)
35 33
Level 1-3 HLA mm
Donor-donor age diff <= 20 yrs
* Based on single factor scoring
Proposed scheme - results
RSS Avon Local Group, 14 October 2008
Factor Maximum possible
% of transplants*
Proposed scheme –
% of transplants
Local exchange 51 47
Sensitised patients (65-100%)
35 33
Level 1-3 HLA mm 49 34
Donor-donor age diff <= 20 yrs
* Based on single factor scoring
Proposed scheme - results
RSS Avon Local Group, 14 October 2008
Factor Maximum possible
% of transplants*
Proposed scheme –
% of transplants
Local exchange 51 47
Sensitised patients (65-100%)
35 33
Level 1-3 HLA mm 49 34
Donor-donor age diff <= 20 yrs
82 78
* Based on single factor scoring
Proposed scheme - results
RSS Avon Local Group, 14 October 2008
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 identifiedThe maximum possible number of transplants will be achieved
Note – at registration, HLA match and donor age requirements can be specified
Agreed national matching scheme
RSS Avon Local Group, 14 October 2008
0
10
20
30
40
50
60
70
80
1-9 10-29 30-49 50-64 65-84 85-100
% sensitisation
% t
ran
spla
nte
d
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 incompatible34% HLA incompatible
Among HLA incompatibles
RSS Avon Local Group, 14 October 2008
Who is most likely to find a match?
Recipient Incompatible Donor
% Identified for Tx
O A 23
O B 18
O AB <5
A B 59
A AB <5
B A 40
B AB <5
Recipient Incompatible Donor
% Identified for Tx
O O 29
A O 73
A A 22
B O 48
B B <5
AB O UTE
AB A 25
AB B <5
AB AB <5
Blood group incompatible Tissue type incompatible
RSS Avon Local Group, 14 October 2008
Where are we now?
RSS Avon Local Group, 14 October 2008
Matching run summary
Run no.
Run date
No. of pairs (potential recipients)
No. of exchanges identified (possible transplants)
No. of transplants resulting
1 Apr 07 9 (8) One 2-way (2) 2
RSS Avon Local Group, 14 October 2008
Matching run summary
Run no.
Run date
No. of pairs (potential recipients)
No. of exchanges identified (possible transplants)
No. of transplants resulting
1 Apr 07 9 (8) One 2-way (2) 2
2 Jul 07 26 (25) One 2-way (2) 2
RSS Avon Local Group, 14 October 2008
Matching run summary
Run no.
Run date
No. of pairs (potential recipients)
No. of exchanges identified (possible transplants)
No. of transplants resulting
1 Apr 07 9 (8) One 2-way (2) 2
2 Jul 07 26 (25) One 2-way (2) 2
3 Oct 07 32 (31) None
RSS Avon Local Group, 14 October 2008
Matching run summary
Run no.
Run date
No. of pairs (potential recipients)
No. of exchanges identified (possible transplants)
No. of transplants resulting
1 Apr 07 9 (8) One 2-way (2) 2
2 Jul 07 26 (25) One 2-way (2) 2
3 Oct 07 32 (31) None
4 Jan 08 66 (65) Three 2-way (6) 2
RSS Avon Local Group, 14 October 2008
Matching run summary
Run no.
Run date
No. of pairs (potential recipients)
No. of exchanges identified (possible transplants)
No. of transplants resulting
1 Apr 07 9 (8) One 2-way (2) 2
2 Jul 07 26 (25) One 2-way (2) 2
3 Oct 07 32 (31) None
4 Jan 08 66 (65) Three 2-way (6) 2
5 Apr 08 76 (73) Two 2-way & four 3-way (16) 2
3-way exchanges considered in April 2008 run onwards, following agreement from the Kidney Advisory Group
RSS Avon Local Group, 14 October 2008
Pooled donation
Donor1
Recip1
Donor2
Recip2
Don
or3
Rec
ip3
Donor4
Recip4
Donor5
Recip5
2-way exchange 3-way exchange
RSS Avon Local Group, 14 October 2008
Matching run summary
Run no.
Run date
No. of pairs (potential recipients)
No. of exchanges identified (possible transplants)
No. of transplants resulting
1 Apr 07 9 (8) One 2-way (2) 2
2 Jul 07 26 (25) One 2-way (2) 2
3 Oct 07 32 (31) None
4 Jan 08 66 (65) Three 2-way (6) 2
5 Apr 08 76 (73) Two 2-way & four 3-way (16) 2
6 Jul 08 85 (80) One 2-way (2) 2 (planned)
RSS Avon Local Group, 14 October 2008
Matching run summary
Run no.
Run date
No. of pairs (potential recipients)
No. of exchanges identified (possible transplants)
No. of transplants resulting
1 Apr 07 9 (8) One 2-way (2) 2
2 Jul 07 26 (25) One 2-way (2) 2
3 Oct 07 32 (31) None
4 Jan 08 66 (65) Three 2-way (6) 2
5 Apr 08 76 (73) Two 2-way & four 3-way (16) 2
6 Jul 08 85 (80) One 2-way (2) 2 (planned)
7 Oct08 123 (115) Six 2-way & three 3-way (21) Not yet known
RSS Avon Local Group, 14 October 2008
Matching run summary
Run no.
Run date
No. of pairs (potential recipients)
No. of exchanges identified (possible transplants)
No. of transplants resulting
1 Apr 07 9 (8) One 2-way (2) 2
2 Jul 07 26 (25) One 2-way (2) 2
3 Oct 07 32 (31) None
4 Jan 08 66 (65) Three 2-way (6)* 2
5 Apr 08 76 (73) Two 2-way & four 3-way (16)* 2
6 Jul 08 85 (80) One 2-way (2) 2 (planned)
7 Oct08 123 (115) Six 2-way & three 3-way (21) Not yet known
* Transplants did not proceed for various reasons
RSS Avon Local Group, 14 October 2008
Blood group composition of October 2008 list
Recipient Blood Group
Total O A B AB
Donor Blood Group
O 26 7 5 0 38
A 43 16 5 1 65
B 6 5 5 0 16
AB 3 0 1 0 4
Total 78 28 16 1 123
Many more A donors than A, AB recipients
RSS Avon Local Group, 14 October 2008
Degree of sensitisation for patients on October 2008 list
Calculated sensitisation (%)
No. of patients
% of patients
0 - 9 27 23
10 - 29 5 4
30 - 49 1 1
50 - 64 11 10
65 - 84 14 12
85 - 94 20 17
95 -100 37 32
Total 115 100
RSS Avon Local Group, 14 October 2008
Future development
Altruistic donor
Pooled donor ‘couple’ - 1
Pooled donor ‘couple’ - 2
Patient on deceased donor transplant list
Domino paired/pooled donation
RSS Avon Local Group, 14 October 2008
Thank You