How do we approach dilemmas in red cell testing?

Despite the large number of serologically identified red cell antigens to date, it is reassuring to note that in the common clinical scenario, the transfusion laboratory would only likely deal with a narrow range of clinically significant antibodies to specific antigens of blood group systems. Accurate ABO and RhD typing still remains the most crucial step in pretransfusion testing followed by the antibody screen. The correct identification of single antibodies or multiple antibodies and whether they are alloantibodies or autoantibodies is necessary so that corresponding antigen-negative red cells can be supplied. Clinically insignificant antibodies or what some would denote as ‘nuisance’ antibodies would need to be differentiated from clinically significant antibodies. When discrepancies occur between forward and reverse ABO typing, it is crucial that laboratories resolve the discrepancy before a specific ABO blood group is assigned. The inclusion of O cells in reverse grouping, anti-H and anti-A1 lectins in the forward, performing the typing on a range of temperatures using washed red cells and careful interpretation of agglutination patterns, would usually provide an answer. On occasions, a saliva test may be necessary and rarely molecular typing. With regard to RhD typing, test systems should identify RhD-negative and D-variant individuals so that D-negative units can be issued to them. Testing with antisera from different clones, the use of adsorption–elution techniques and RhD.CcEe typing aids in coming to a conclusion, before molecular testing becomes necessary. Extended red cell phenotyping is indicated if the patient is at risk for developing a red cell antibody.