Inexplicable donors
Inexplicable donors or CBUs are records that have HLA that cannot be explained by a combination of two haplotypes in the haplotype frequency (HF) set for the population that the donor or CBU is part of.
Because the HLA typing of this donor/CBU cannot be explained, the matching algorithm is unable to calculate match probabilities. If these donors/CBU's have any ambiguity in their typing, these records appear on the bottom of the match class that they are part of (e.g. 10/10, 9/10, 7/8). 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. When there is no ambiguity then the donor will appear at the top of its match class.