The Laboratory of Immunohematology & Genomics screens blood samples to identify donors whose RBCs lack a high prevalence antigen. Once identified, the donor is assigned the rare donor group identifier, which is known as Code 99.

Pertinent information is entered in the computer and a hard copy of the record is forwarded to Special Donor Services Department who maintains and monitors the future contact of these rare donors. Future RBC donations of these donors are sent directly to a patient in need or to the Frozen Laboratory for preservation until needed by a patient.

These rare types can be unique to each specific ethnic background. Donor samples are tested for special antigens based on their ethnicity. A unit of blood is considered rare when more than 200 donors have to be screened to find 1 suitable donor.

Completely typed antigen-negative units (referred as Code 96) are provided by the Testing Laboratory to the Laboratory of Immunohematology to be issued for patients with red cell antibodies. These donors are referred as precise-matches to patients who have developed red cell antibodies. These donor units are not only typed for ABO but also typed for the antigens of the following blood group systems: RH, K, FY, JK, Ss. They are categorized according to their Rh phenotype (R1R1, R2R2, RoRo and rr.) and lack different combinations of blood group antigens.