Impact on patient of the detection of weakly expressed RhD antigens in blood donors.

Due to blood transfusions, pregnancy, and organ/tissue transplants or grafts,1 red blood cell alloimmunization may lead to serious complications, such as hemolytic transfusion reactions,2–4 which have been regarded as one of the most frequent causes of transfusion-related deaths in recent years according to reports from the Food and Drug Administration (FDA).5 Rh, the most complex blood group system, has the highest clinical importance after the ABO group.6,7 The D antigen, found in Rh-positive individuals, is the most important in the system as it is the most immunogenic.7,8 Therefore, given the risk of alloimmunization, RhD-positive red blood cells must not be transfused to RhD-negative patients except in emergencies involving massive hemorrhage when RhD-negative units are not available.7 The RhD protein has 417 amino acids divided into seven intracellular segments, twelve transmembrane segments and six extracellular segments.9 Amino acid substitution in the intracellular or transmembrane segment of the RhD protein leads to weakening of the D antigen expression in the membrane of red blood cells resulting in a weak D phenotype.6–13 Hence, weak D testing must always be performed in blood