Monday, May 19, 2014

Deceased Donor Kidney Allocation 2014


In the USA in June 2013 the OPTN/UNOS Board of Directors approved amendments to the OPTN policy for deceased donor kidney allocation. These ideas have been discussed for the last 9 years and Nate wrote about some of these ideas here and posted a poll here. The central premise for the changes were outlined in a press release on the OPTN website here. The exact dates for nation wide implementation are not currently available.

Longevity-matching

This is the main and most interesting part of the new system.
Priority will be given to transplant recipients most likely to live the longest post transplant. Each recipient is given an EPTS (estimated post-transplant survival) score ranging from 1 to 100%. This score is calculated from recipient characteristics; Age, years on dialysis, presence of diabetes and prior solid organ transplant.
Here is the OPTN online EPTS calculator
Remember the EPTS score needs to be updated daily.

·      The lower percentage EPTS score the longer estimated survival.

Recipients in the top 20th percentile will be prioritized for the best kidneys, that is kidneys with a KDPI (Kidney Donor Profile Index) of less than 20%. The KDPI is a re-working of the Kidney Donor Risk Index, which is a risk quantification score defined in a study published by Rao et al in 2009. The KDRI expresses the relative risk of kidney graft failure for a given donor compared to the median kidney donor from the previous year. Values greater than 1 have higher risk of failure. A KDPI of 80% means that the donor kidney has a greater chance of graft failure than 80% of all kidneys retrieved in the previous year.
The KDPI is calculated using 10 donor characteristics; donor age, height, weight, ethnicity, history of hypertension and diabetes, cause of death, serum creatinine, hepatitis C status, and donation after circulatory death status.
The equation is complicated but here is the OPTN online KDPI calculator.

·      The lower the KDPI the better the kidney.

These two concepts will replace the current categories of SCD and ECD.
SCD will be the equivalent of KDPI of 85% or less. ECD will be equivalent to greater than 85%.

Waiting time calculation

With the new rules the waiting time will be calculated from when the recipient reached a GFR of 20ml/min or less or when they started on RRT even if they were listed after this. Thus, waiting times will be backdated. Waiting time points will be score as fractions of a year, number of days divided by 365.

The current system assigns the wait time when the candidate is listed.

Access for highly sensitized recipients

The new system includes additional priority for recipients that are highly sensitized. This is a sliding scale points system based in calculated PRA starting at a CPRA of 20%. Points on this scale are weighted significantly in favour of those with CPRA over 98%. 
The new system will also facilitate the offer of kidneys from certain blood type A donors (A2 and A2B) to type B recipients in an effort to reduce the wait time for these recipients.

CPRA (%)
Points
0–19
0
20–29
0.08
30–39
0.21
40–49
0.34
50–59
0.48
60–69
0.81
70–74
1.09
75–79
1.58
80–84
2.46
85–89
4.05
90–94
6.71
95
10.82
96
12.17
97
17.3
98
24.4
99
50.09
100
202.1


Wider sharing

The ‘payback’ rule will be removed. If a local service receives a well-matched kidney from another donation service they will no longer ‘owe’ a kidney.

Priority point system for new kidney allocation

This scoring system is used to rank recipients in four quartiles of KDPI.
KDPI <20%; 21 – 34%; 35 – 85%;  >85%

Within each quartile there is also a kidney allocation classification system based on location/OPO, ABDR mismatch, CPRA and blood group.

It is my understanding that EPTS determines which quartile a recipient is ranked in.

Factor
Points Awarded
For qualified time spent waiting
1 per year
(as (1/365 per day)
Degree of sensitization (CPRA)
0–202
Prior living organ donor
4
Pediatric candidate if donor KDPI 35%
1
Pediatric candidate (age 0–10 yr at time of match) when offered a zero antigen mismatch
4
Pediatric candidate (age 11–17 yr at time of match) when offered a zero antigen mismatch
3
Share a single HLA-DR mismatch with donor
1
Share a zero HLA-DR mismatch with donor
2

This new system seems fair and is an effort to get the most out of each kidney transplanted. It also attempts to get more use out of poorer quality kidneys by more inter OPO sharing.
The full UNOS policy 3.5 statement can be found here.

2 comments:

Phil Gauthier said...

The quartiles you refer to at the end are based on donor KDPI, not recipient EPTS. The quartiles determine how the kidneys are distributed:

KDPI 0-20 : patients with EPTS score in top 20%, pediatrics
KDPI 21-35 : pediatrics (replaces old share 35 system, basically instead of kidneys from donors younger than 35 going to kids it's now donors with KDPI scores of 35 or less.)
KDPI 36-85 normal distribution
KDPI> 85: the new ECD, patients must consent. Otherwise no change in distribution.

Whether or not the EPTS score changes waiting times is interesting, theoretically the best 20% of donors will go to the best 20% of recips, so waiting time won't change. However some of these recipients may also accept kidneys from higher KDPI donors, so their waiting time overall may decrease.

Andrew Malone said...

Thanks for your comment Phil.
I understand the quartiles are based on KDPI. Which recipients get put into each KDPI quartile depends on the recipients EPTS as you have explained. IE those with a good EPTS (20% or less) get matched with good KDPI kidneys (KDPI 20% or less). I will change the quoted KDPI quartiles to percentages to avoid confusion.