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titleWhy are there sometimes probabilities missing?

This can have several causes.

  • Overall match probabilities and locus-specific match probabilities are missing: this is most likely because the HLA typing of the donor/CBU is not consistent with any known haplotypes for the population that the donor is in (inexplicable donor). Without haplotypical context, the matching engine is not able to provide match probabilities. 
  • Only locus-specific match probabilities are missing: It does not make sense to display the probability of match for a specific locus in case of a mismatch
    • Because the known match probability is 100% and therefore there is no probability of a(n additional) mismatch and therefore displaying match probabilities in case of an additional mismatch does not make sense.
    • Because the probability of an additional mismatch is 0% for another reason, e.g. because the donor is low resolution typed at 3 loci and therefore in theory be a match, but it is very unlikely.  

See the following page for more information: Feature differences Hap-E Search vs Optimatch

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titleWhat are inexplicable donors/CBUs?

At the top of search results you can see how many donors or CBUs are inexplicable. 
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Inexplicable donors or CBUs are records that have HLA that cannot be explained by a combination of two haplotypes in the haplotype frequency set (Haplotype frequency sets in the HAP-E matching algorithm of the Search & Match Service) for the population that the donor or CBU is part of. To find out which haplotype frequency set was used, you can use the full report

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The number there corresponds to the set on the Haplotype frequency sets in the HAP-E matching algorithm of the Search & Match Service share page. 

Because the HLA typing that this donor/CBU has cannot be explained, Hap-E also cannot calculate match probabilities. Currently these donors appear on the bottom of the match class that they are part of (e.g. 10/10, 9/10, 7/8). We are working on a way to move potentially relevant but inexplicable donors to a better place in the search results. 

The number of inexplicable donors/CBUs mentioned therefore serves as a reminder that there are potentially relevant search results available that can be found at the bottom of the match class. 



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titleWhy is, for example, a donor with B*15:BPXE not shown as a potential match for a patient with B*15:03?

Since B*15:BPXE = B*15:03/61/74/103 a donor with this codes is a potential allele match for the patient. According to the official WMDA serology/DNA correspondence table, B*15:61 and B*15:74 have a serology of B15/B70 while B*15:03 is B72 and B*15:103 is B70. As a consequence a serology of B15 rules out B*15:03 and this donor is no longer potentially identical (on the allele level). Another explanation could be the limited length of donor lists.

Background: Unfortunately, for many donors serology was derived from DNA (by using the first field for the serological assignment) and vice versa (by appending “:XX” to the serological assignment) and often eventually both values are reported. In the case discussed, B*15:BPXE probably was translated back into B15 which is most likely wrong. This is a typical and (with certain registries) frequent case but there are many more unexpected DNA-serology correspondences that can give rise to exactly the same situation.

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