Rare red blood cells (RBCs) can be used in antibody identification or compatibility testing when antibodies to high-prevalence antigens or to other rare phenotypes are suspected. These rare RBCs are typically not readily available in commercial reagent RBC panels. When such RBCs are identified in donors or patients, however, laboratories can freeze and store the RBCs in a glycerol solution, which prevents severe freezing injury. When needed, the glycerolized RBCs can be thawed and the glycerol removed using decreasing concentrations of NaCl. The rare RBCs can then be used in testing.