The following links list how search determinants are assigned to each HLA allele by the different registries; The Anthony Nolan, the NMDP, BMDW, Canadian Unrelated Bone Marrow Donor Registry, France Greffe de Moelle, BBMR and also the ZKRD approach to search determinants.
In the HLA hierarchy of the Anthony Nolan matching program, antigens and alleles are assigned to either the broad antigen or the serological split, these being the equivalent of search determinants. If assigned to the serological split, the matching program will also include in the report those donors with alleles assigned to the broad antigen and with alleles assigned to any other split of that broad antigen, arranged in ascending order of match. Antigens, alleles and NMDP codes can only each be assigned to one search determinant. Hence, in the situation where a patient or donor has a string of possible alleles at a locus i.e. intermediate type designated as NMDP code, the string can only be assigned to one search determinant. HLA types to be entered on the system are only valid if all their component alleles are recorded in the HLA hierarchy. This creates the situation in the present system where null alleles have to be assigned to the search determinant indicated by their first two digits. If they were not, HLA types with strings containing null alleles would be rejected, because part of the string (the null allele) would not appear in the HLA hierarchy.