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

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


Background


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


• 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


Stages involved in the UK paired donation scheme


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


1

2

34

5

Matching processStage 2: Determine all combinations of

exchanges


1

2

34

5

1

2

34

5


exchanges


1

2

34

5

1

2

34

5

1

2

34

5


exchanges


1

2

34

5

1

2

34

5

1

2

34

5

1

2

34

5


exchanges


1

2

34

5

1

2

34

5

1

2

34

5

1

2

34

5

1

2

34

5


exchanges


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


1

2

34

5

1

2

34

5 X

X

Matching processStage 3: Optimum combination


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


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

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

Simulations


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


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


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



% of transplants*

Proposed scheme –

% of transplants

Local exchange 51 47


Level 1-3 HLA mm






% of transplants*

Proposed scheme –

% of transplants



35 33

Level 1-3 HLA mm






% of transplants*

Proposed scheme –

% of transplants



35 33

Level 1-3 HLA mm 49 34






% of transplants*

Proposed scheme –

% of transplants



35 33

Level 1-3 HLA mm 49 34


82 78




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


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


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


Where are we now?


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



Run no.

Run date




1 Apr 07 9 (8) One 2-way (2) 2

2 Jul 07 26 (25) One 2-way (2) 2



Run no.

Run date




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



Run no.

Run date




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



Run no.

Run date




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


Pooled donation

Donor1

Recip1

Donor2

Recip2

Don

or3

Rec

ip3

Donor4

Recip4

Donor5

Recip5

2-way exchange 3-way exchange



Run no.

Run date




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


6 Jul 08 85 (80) One 2-way (2) 2 (planned)



Run no.

Run date




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



7 Oct08 123 (115) Six 2-way & three 3-way (21) Not yet known



Run no.

Run date




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


7 Oct08 123 (115) Six 2-way & three 3-way (21) Not yet known

* Transplants did not proceed for various reasons


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


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


Future development

Altruistic donor

Pooled donor ‘couple’ - 1

Pooled donor ‘couple’ - 2

Patient on deceased donor transplant list

Domino paired/pooled donation


www.uktransplant.org.uk

[email protected]


Thank You

Documents

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