Diagnosis: Immunohematology: Pretransfusion testing
• To calculate the number of units that need to be screened to find n compatible units, divide n by the probability of finding one compatible unit. For example, 44 red cell units will have to be screened to find 10 compatible units for this patient (10/0.23=44).
• Most RhD-negative individuals are also negative for the C- and E antigens (ce/ce phenotype); thus, RhD-negative units will typically be compatible with patients who have an anti-C or anti-E in plasma.
• To calculate the probability that a random donor unit is compatible for a patient with multiple alloantibodies, multiply the probability of compatibility for each antigen for which the patient has an antibody against.
• Table 3 shows the approximate probability that a random donor unit is compatible (i.e., the probability that the donor unit is antigen-negative):
• Enzymes such as ficin and papain DiMiNish expression of Duffy, M-, and N antigens, enhance expression of Rh and Kidd antigens, and do not affect K antigens.