Unlike red blood cell groups, there are enormous numbers of possible tissue types and it takes an extremely large register of unrelated donors to find a match for each patient. In spite of access to over three million donors worldwide, some searches are still not successful. Male donors, and donors from Ethnic Minorities, are particularly needed by the Trust. Male donors are usually preferred for a variety of clinical reasons. As tissue type is an inherited characteristic, patients tend to find a match from someone in the same Ethnic group.
Some Ethnic minorities are desperately underrepresented on the register.