NHS BLOOD AND TRANSPLANT
Incompatible Pairs Living Donor Kidney Application
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INTRODUCTION
1.1
The National Living Donor Kidney Sharing Scheme (NLDKSS), commonly
known as the paired pool, allows incompatible pairs the opportunity to ‘swap’
kidneys with other pairs. Due to its recent inception and the way the matching
process works, it is difficult for patients to know how likely they are to get a
transplant through the scheme. This application is able to give patients an
estimate of how long they can expect to wait for a transplant given their and
their donor’s relevant characteristics. Information is also given about expected
waiting time for a deceased donor kidney transplant and chances of
incompatible transplant for the patient to compare all of their possible routes to
transplant.
1.2
The Incompatible Pairs Living Donor Kidney Application is based on a
statistical analysis carried out by the Statistics and Clinical Studies
Department within NHS Blood and Transplant.
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STARTING UP THE APPLICATION
2.1
The Incompatible Pairs Living Donor Kidney Application was developed in
Microsoft (MS) Excel Professional Edition (2010). To use the software MS
Excel 2003 or later versions will be required although there may be other
conversion software available capable of running this program.
2.2
Macros and security settings: On opening the software in MS Excel, and
depending on your security settings, you may be prompted to “Enable Macros”
or you may be presented with a warning message that alerts you to the fact
that the software has embedded macros. If you do not choose to enable or
accept macros then it will not be possible to use this software. If security
settings are set at ‘High’ the software can still be used but you may not be
able to make use of the ‘Reset’ button embedded within the software.
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USER INSTRUCTIONS
3.1
Once opened, the screen should look like that shown in Figure 1.
Figure 1:
3.2
Opening screen shot
On the left hand side of the screen you will see a number of drop-down boxes.
A selection must be made in each relevant drop-down box before a result will
be shown.
3.3
To help select the correct information, further information on each of the
variables listed can be found in the definitions section that follows. Once all
the relevant information has been selected the software should present the
results almost instantaneously. If you would like to reset all variables simply
press the reset button.
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DEFINITION OF INFORMATION REQUIRED
Recipient Blood Group: O, A, B or AB.
Calculated Reaction Frequency: Standardised calculated reaction
frequency, defined in 3 groups: 0-84, 85-94 and 95-100.
Donor Blood Group: O, A, B or AB.
ABOi TX with willing Donor: The clinician should decide whether, based on
ABO titre levels, the pair could proceed with an ABO incompatible transplant
in line with the practices at that centre. Selecting ‘Low Titre’ will indicate that
such a transplant is likely to be able to proceed. Selecting ‘High Titre’ will
indicate that this is not possible and therefore relevant transplant survival
information will not be given. This field is only relevant when the nature of the
incompatibility of the pair is blood group incompatibility and there is a ‘Not
Applicable’ option that can be selected if this is not relevant.
HLAi TX with willing Donor: The clinician should decide whether, based on
Mean Fluorescence Intensity values, the pair could proceed with a HLA
incompatible transplant in line with the practices at that centre. Selecting ‘Low
DSA’ will indicate that such a transplant is likely to be able to proceed.
Selecting ‘High DSA’ will indicate that this is not possible and therefore
relevant transplant survival information will not be given. This field is only
relevant when the nature of the incompatibility of the pair is HLA
incompatibility and there is a ‘Not Applicable’ option that can be selected if this
is not relevant.
Recipient Age: Current recipient age, split into 5 groups: 18-30, 31-40, 41-50,
51-60, 61+.
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INTERPRETING THE RESULTS DISPLAYED
5.1
An example of how the results are presented is shown in Figure 2 and an
explanation of how to interpret the results is shown in paragraphs 5.2 to 5.3.
Figure 2:
Example results
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5.2
Estimated Chance of Transplant:
The table indicates that for recipients with those characteristics, 11-20% are
typically transplanted within just 1 year of listing on the deceased donor
waiting list. For donor-recipient pairs with those characteristics, around 6170% are typically transplanted within a year through the NLDKSS. Figures are
also given for 6 months and 3 years. In this case we also see that the
indication of ‘Low Titre’ in the ABOi TX variable means that a blood group
incompatible transplant is likely. Waiting times are not given in this case as the
time to transplant involves the (short) work up time to transplant only.
5.3
Transplant Survival Rates
This table indicates that for deceased donor transplants in recipients with
those characteristics, around 91% of transplants are still surviving after 1 year.
Data is similarly given for living donor transplant (96%) and ABO incompatible
transplant (92%). No data is given for HLA incompatible transplant as that
information is not relevant for this pair.
NHS Blood and Transplant
2015
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Statistical Methodology for Chances of Transplant and Transplant
Survival Rate Estimation
Computing estimated chance of transplant
For the deceased donor waiting list, waiting times were calculated using existing data
from the national transplant database. Patients were selected that had characteristics
that were similar to those who have entered the NLDKSS. This gave us waiting times
from the deceased donor waiting list for a cohort similar to patients in the NLDKSS.
This similarity was based on variables that are relevant in the NLDKSS. These are
blood group, calculated reaction frequency and age. Cox Proportional Hazards
models were then used to give survival curves that can be interpreted as chance of
transplant.
To estimate waiting time to transplant in the NLDKSS, simulations were used. The
simulations were performed in order to obtain more data than is currently available as
the scheme has only been in its current form since 2012. Data from pairs and
altruistic donors that have entered the scheme were selected randomly with
replacement to join the simulated scheme. Matching runs were performed that
simulated 3 years in the scheme, and this was repeated 10 times. Pairs could drop
out of the scheme with a fixed probability, and potential transplants could fall through
with a fixed probability that was based on the proportion of those that fell through in
the scheme. Registration time before first matching run and time to transplant after
identification of a potential transplant were selected at random from real data. Cox
Proportional Hazard models were then used to estimate time to transplant.
Computing transplant survival rates
A Cox Proportional Hazards model was used to determine the probability of
transplant survival for each patient based on their individual risk factor values.
Transplant survival looks at the survival of the graft and the patient until either graft
failure or death. Observations are censored if the graft is functioning and the patient
is alive at the last time point. The factors included in this model were recipient age
group and transplant type (deceased compatible, living compatible, living blood group
incompatible and living tissue type incompatible).
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