In the legacy version of Search & Match Service, search coordinators were limited and could see 2,000 results potential matches when they initiated a search. Following popular demand, WMDA makes it possible for search coordinators to view ALL potential stem cell sources when a search is initiated with the added relief of pagination to allow your browser to load the results faster.
WMDA has received feedback from users search coordinators who are receiving an overwhelming number of results potential matches and find it difficult to identify the most relevant stem cell source for their patient. It is important to make a distinction between "relevant" and "suitable" when it comes to donor search. While the algorithm returns all possible potentially matched donorsstem cells sources, you would like to view the most relevant donors stem cell sources toward the top of the match list based on their probability to be HLA-matched for your patient. However, match grade might not always be the only parameter for donor selection and thus donor suitability based on non-HLA factors and the patient's clinical status should also be considered.
The more variability (HLA mismatches, considered loci or untyped loci) you allow in your search, the more potential donors and/or CBUs cord blood units will be returned by the algorithm. You might also notice results being returned that seem to be an obvious mismatch. This most commonly occurs when the patient is homozygous at one or more loci and the typing for the donor contains a null allele. Since a homozygous typing is generally considered a match with a donor that has one allele that matches the homozygous patient typing and the other is a null allele, Hap-E returns this donor/CBU cord blood unit as a potential match. Please see the slide below from a recent webinar:
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The way those results are originally sorted in the browser is determined by WMDA, not the algorithm, and can be adjusted by you to sort the results you deem relevant, on a case by case basis. Please keep in mind that an algorithm designed for probability matching will just calculate "chances" and you should use it as a tool in combination with your own knowledge of HLA and the transplant centre's (TC) preferences for the patient. Do not select donors/CBUs cord blood units solely on the probabilities calculated by the system. You can read more about haplotype frequencies here.
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In the legacy system when running a standard donor search, all returned donors have values for HLA-A, -B and -DRB1. This is different when running a search in the new system. There all donors need to have typing at HLA-A, -B and at least one other locus (which may or may not be HLA-DRB1). This means that donors are returned in the new system and/or cord blood units are shown on the match list that do not have typing at HLA-DRB1. This typically explains the majority of the difference in number of search results as mentioned in the search summary. Although in some cases these donors with typing at HLA-A, -B and -C or -DQB1 may prove useful, in most cases they are not. We therefore apply a default filter to all search results.
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