Technical Specifications

Proposed new algorithm: technical specifications

A universal continuous points allocation score is calculated as the sum of points awarded for each of the following attributes:

1. Waiting time

2. HLA match quality

3. PRA bonus

4. Prognosis match bonus

5. Same state bonus

6. If applicable: National urgent bonus, State priority bonus, Prior living donor bonus, or kidney-after-other-organ bonus

Interstate shipping is allowed when the total score is at least as high as the shipping threshold, or if there are no local recipients.

The shipping threshold is a floating threshold that depends on the net debt between states and is calculated as 12 - 0.5 x net kidneys owed to recipient state, with a maximum value of 15.

If recipient score >= shipping threshold OR the recipient is within the same state as the donor, 100 points are added to the final score to ensure interstate recipients below the shipping threshold never outrank a same-state recipient. This effectively creates a separate tier equivalent to the interstate utilisation tier in the current allocation system.

For example, for a donor arising in WA:

Points calculation for each component of the allocation score

1. Waiting Time

Measured in years, not rounded, not weighted.

days since dialysis start

362.25

2. HLA match quality

The intention of the HLA-match quality adjustment is to identify and prioritise what would constitute a good HLA-match for a given patient, considering the potential donor pool and the recipient’s HLA-profile.

An “ABDRDQ mismatch score” is calculated to assess the HLA-match quality of individual donor-recipient pairs, based on the total number of Class I and Class II mismatches:

Each A mismatch = 1 point

Each B mismatch = 1.5 points

Each DR mismatch = 3 points

Each DQ mismatch = 3 points

ABDRDQ mismatch score = total (range 0-17 points)

For each patient, the square root of their ABDRDQ mismatch score versus a reference pool of 1000 donors is calculated. The mean and standard deviation (SD) of this sqrt(score) is calculated and stored in OrganMatch for reference.

For each individual potential donor-recipient combination, the square root of their ABDRDQ mismatch score is calculated and compared against the recipient’s mean and SD (versus the reference population) to calculate a z-score, as follows:

Notes on this score:

ABDRDQ score = the weighted sum of the number of mismatches at the A/B/DR/DQ loci
Weights for calculating the A/B/DR/DQ score: 1:1.5:3:3
Mean = the mean of the square-root ABDRDQ mismatch scores calculated versus a reference panel of 1000 donors
SD = the standard deviation of the square-root ABDRDQ mismatch scores calculated versus a reference panel of 1000 donors
The mean score is calculated against the entire reference panel, not restricted to within blood group
The mean score is calculated when a patient is listed, and the mean and SD are stored in OrganMatch
The HLA match quality score is adjusted by a recipient age-dependent scaling factor that gives the most emphasis to good HLA matches in younger recipients
Age-based tapering does not fall all the way to zero because it is still worth prioritising a perfectly matched 65 year-old ahead of a mismatched 65 year-old, for example, all other parameters being roughly equal

Age dependent scaling factor

3. PRA bonus

Calculated as: 1 x (mPRA/100) + 29 x 0.8^(100-mPRA)

Range 0 to 30. The parameters are: maximum 30, linear component 1, decay parameter 0.8.

4. Prognosis match bonus

Calculated as: 3 x (EPTS^2-101x|EPTS-100x(EPTS-KDPI)|+10000)/9900

Score quantifying the degree of KDPI-EPTS matching. Maximum value of 3.

5. Home state bonus

If the donor and recipient are in the same state, 1 bonus point is given. For all other recipients, this is set to 0.

6. Urgent or priority bonuses

National Urgent

The “National Urgent” category applies to medically urgent cases (e.g. imminent loss of dialysis access, approved by RTAC) and to orphaned ANZKX patients. This category receives 15 bonus points and access to all ABO compatible kidneys.

State Priority

The “State Priority” category applies to cases where an individual state Advisory Committee – for whatever reason – approves additional priority for that patient at the state level. This category receives 12 bonus points for donors within their state only. Normal ABO rules apply.

Prior Living Donor

Prior living donors receive 10 bonus points.

Kidney-after-other organ transplants

Patients requiring kidney transplantation shortly after heart, lung, or liver transplantation (according to eligibility criteria and protocols specified by the relevant Advisory Committees) receive 12 bonus points.

Shipping rules

Interstate shipping is allowed when the total score is at least as high as the shipping threshold, or if there are no local recipients.

The shipping threshold is a floating threshold that depends on the net debt between states and is calculated as (12 - 0.5 x net kidneys owed to recipient state), with a maximum value of 15.

Blood group compatibility rules

Proposed rule:

ABO identical transplants are always allowed.
A to AB transplants are allowed if the combination of points for HLA match quality adjustment, PRA bonus and prognosis match is at least 5
O to B transplants are allowed if the combination of points for HLA match quality adjustment, PRA bonus and prognosis match is at least 12
All other ABO non-identical transplants are allowed if the combination of points for HLA match quality adjustment, PRA bonus and prognosis match is at least 18.

Other rules

Interstate utilisation offers with rank above 20 do not count towards state debt calculations.
Tie-break rule in the event that two potential recipients have identical scores:

Same state
ABO identical
Waiting time
Age-HLA match points
PRA
Prognosis matching
Random.

Multi-organ transplants

SPK transplants

When a suitable pancreas donor arises, one of the kidneys will also be allocated with the pancreas UNLESS there are two potential kidney-only recipients with raw allocation scores of 15 points or higher.

SPK patients can also be dual listed on the kidney-only list and – if offered a kidney through the kidney list – the pancreas can also be requested. For SPK patients on the kidney-only list, 2 bonus points are to be added to their kidney allocation score if they accept the pancreas along with the kidney offer

Other multi-organ transplants

Offers for simultaneous kidney-liver, kidney-heart and kidney lung transplantation are to be made prior to offers to the kidney-only list (as per the status quo).