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:
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.
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.
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