Calculator results display:
-
cRF - calculated reaction frequency
- Mp - calculated matchability point
- Fm - favourably matched donors
- Ad - available HLA compatible donors in the selected pool
- A all 10,000 donors
- D only donors with HLA-DPB1 types
Pool selects the donor blood groups every figure is counted over. It defaults to Identical, the
calculation the official calculator performs.
Donor pool:
The calculation scores against blood group identical donors, as the official calculator does. Kidney allocation
policy offers several recipients compatible non-identical donors as well, and which ones depends on their tier.
| Recipient | Identical | Tier B | Tier A |
|---|
| O | O | O | O |
| A | A | A | A+O |
| B | B | B+O | B+O |
| AB | AB | AB+A | AB+A+O |
Tier is an input, not something the calculator can work out: the 7 year waiting rule is patient data it never sees.
Blood group B and AB patients are offered non-identical donors in both tiers, so Identical is the only
setting that reproduces the value NHSBT holds for them.
cRF, Fm and Ad are sound over any
pool. Mp is not. It is a decile rank built from blood group identical counts, so
a count drawn from a wider pool reads low against it — a blood group AB patient whose true score is 6 reads as
1, the easiest band. The score is shown with a warning rather than hidden, but it should not be compared with the
score on the waiting list.
Allele level HLA-DP4:
The donor cohort records HLA-DP at broad antigen level, so DPB0401 and DPB0402 cannot be scored
against a donor column. Selecting one scores it against the expected carriers of that allele among the DP4 donors,
following the approach NHSBT takes for these two specificities:
cRF = (S + f × D) / N
where N is the donors in the selected pool, S those excluded by the patient's other specificities,
and D the further DP4 donors only the DP4 entry excludes.
The carrier fractions f are
DPB1*04:01 0.86, DPB1*04:02 0.26,
from HLA-DPB1 typing of 456 UK deceased solid organ donors.
Selecting DPB4, or both alleles together, resolves the entry to the broad antigen. Only
cRF is weighted: Mp and Fm count
whole donors, and score an allele entry as broad DP4.
Matchability point bands:
| BG |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
| A |
360 |
279 |
228 |
178 |
146 |
115 |
87 |
63 |
19 |
0 |
| B |
70 |
54 |
42 |
35 |
29 |
24 |
19 |
14 |
6 |
0 |
| O |
405 |
311 |
247 |
193 |
157 |
128 |
103 |
74 |
34 |
0 |
| AB |
23 |
14 |
10 |
8 |
6 |
3 |
|
2 |
|
0 |
For each blood group, patients are assigned to an
Mp
band based on the maximum number of favourably matched donors (Fm) they have. The
Mp bands are defined by specific Fm
threshold values as outlined in the table above.
These thresholds were derived from blood group identical counts, which is why the score is not comparable
over a wider Pool: the same patient's count grows with the pool and so reads against the wrong end of this
table.
NB: The banding is subject to change as the calculator is updated by NHSBT-ODT. There is no set schedule.
HLA type for matchability calculation:
Matchability estimates how many levels 1 and 2 mismatched, HLA-compatible donors (a.k.a. favourably matched donors,
Fm) are available for a patient within the 10,000 donor cohort. They are counted over
the selected Pool: ABO-identical by default, or the blood groups policy offers.
The calculation is based on broad HLA specificities. For determining favourable matches (levels 1 and 2),
only HLA-B and DRB1 are needed: HLA-A does not affect this categorisation.
| HLA mismatch levels for HLA-A, B and DR |
| Level |
Summary |
Combinations included |
| 1 |
000 |
000 |
| 2 |
[0 DR and 0/1 B] or [1 DR and 0 B] |
100, 010, 110, 200, 210, 001, 101, 201 |
| 3 |
[0 DR and 2 B] or [1 DR and 1 B] |
020, 120, 220, 011, 111, 211 |
| 4 |
[1 DR and 2 B] or [2 DR] |
021, 121, 221, 002, 102, 202, 012, 112, 212, 022, 122, 222 |
Ref:
NHSBT-ODT Kidney Allocation Policy - POL186