In general, the majority of the population has one of the ABO blood groups and is Rh positive or negative. There are >200 minor blood groups and >600 known antigens besides A, B and Rh. Because blood groups are distributed differently in different ethnic groups, finding a blood donor with the exact same blood type is a huge challenge. A rare blood donor phenotype occurs 1/1000 and includes high-frequency-antigen-negative and multiple-common-antigen-negative blood groups. Examples of rare blood types include Rhnull, Bombay (Oh) and Junior (Jr) a-. To prevent shortages of rare donor blood units, red cell donations can be frozen for future use. Therefore, it is of high importance to have an accurate international database of rare blood donors to ensure that patients who require lifesaving rare blood units are able to receive them.