The aim of this study was to search for the partial D phenotype in Moroccan blood donors with weak D expression. The study included 32 samples with weak D phenotype, and partial D category red blood cells were detected with the D-Screen Diagast kit, which consists in 9 monoclonal anti-D antibodies specific for the most common categories of partial D. Among the 32 samples studied, we identified 13 specific reactions to a partial D antigen (3 DVI, 2 DVa, 2 D, and 6 DVII), with 8 reactions suggesting a weak D and 11 reactions providing no formal argument in favor of a partial D antigen. This work can be used to validate the performance of the anti-D reagent and to improve the safety of transfusion of red blood cells from donors expressing the partial D antigen by integrating the finding into the recipient file with a recommendation concerning the appropriate care. 1. Introduction Rhesus is one of the most important and clinically significant blood group systems. D antigen (ISBT 004.001; RH1) is the most immunogenic and clinically important of this system because of the ability of anti-D to cause transfusion reactions and hemolytic disease of the foetus and newborn. The Rh system was described for the first time in 1939 and is now considered to be a mosaic of epitopes (antigenic determinants). Partial D variants lack one or more epitopes of D antigen while weak D variants have all epitopes present but express a significantly reduced amount of D antigen per red blood cell and are usually identified by the indirect antiglobulin test (IAT). Partial D and weak D are the most commonly found D variants. Individuals whose red blood cells do not carry all the parts of the D mosaic can, when exposed to the full D antigen, produce anti-D alloantibodies directed against one or more of the missing epitopes, thus defining the phenotype “partial D.” Loss of D epitopes is associated with either gene rearrangements or point mutations affecting extracellular portions of the RhD protein [1, 2]. The great diversity of D variants (weak D and partial D) explains the discrepancies noted between two serological determinations and the lack of reactivity of certain variants by serology [3]. It is very important to identify a donor having a D variant (weak D or D partial D) since in some instances these red blood cells can trigger an immune response if transfused to a recipient who is D negative. The study of D variants in blood donors for immunohematological qualification was little studied in Morocco and thus in order to provide elements of information on the prevalence of weak D
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