PF811 PREVALENCE OF RHD VARIANTS AMONGST A PORTUGUESE BLOOD DONOR CENTRE

Background: Rh blood group system is the most clinically relevant following ABO. The RhD antigen is the most immunogenic since up to 80% of RhD negative persons receiving RhD positive blood from transfusion can develop anti‐RhD and RhD negative women are at risk of haemolytic disease of foetus and newborn if carrying a RhD positive foetus. RHD gene expresses a RhD protein. However, there are more than 275 different RHD alleles reported, resulting in some form of altered RhD protein expression, the D variants. About 85% of European individuals are RhD positive, and an estimated 1% to 2% carries alleles that encode altered D antigens. There are three types of D variants, quantitative or weak RhD(WD), qualitative or partial RhD (PD) and DEL. Aims: We characterized the RhD variants within our blood donor population during a four‐year period. Methods: Blood donors were RhD typed using microplate technology DiaMed‐MP Test (clones TH‐28 IgM; MS‐201/MS‐26 IgM/IgG) and ID card system Diaclon ABO/D (DVI+, DVI‐); RhD negative confirmation was performed using a monoclonal Anti‐D (ID‐Diaclon Anti‐D clone ESD1 IgG) and Coombs‐IgG rabbit ID‐card. All systems from Biorad (Cressier sur Morat, Switzerland). Discrepant samples were sent to the Immunohaematology Reference Laboratory of the Portuguese Blood and Transplantation Institute, for serological and molecular characterization of D variants. Results: There were 3765 first‐time donors during the study period. Ninety‐two samples (2.4%) were identified as D variants, 91 WD and one PD (DBT type 2). The most prevalent WD identified was WD type 3 in 50 individuals (54.9%). This was followed by WD type 4.0/4.1 in 20 donors (22.0%), WD type 2 in 11 donors (12.1%) and WD type 1 in 4 donors (4.4%). Three donors (3.3%) where WD type 4.2/DAR and two (2.2%) were WD type 38. Correlation of WD type and haplotype was analysed: 4/4 donors’ WD type 1 were CDe ; 11/11 WD type 2 were cDE ; 47/50 WD type 3 were CDe (two were CDe/cDE and one cDe ); 18/20 WD type 4.0/4.1 were cDe (two were CDe / cDe ); and 3/3 WD type 4.2/DAR were cDe . The two donors WD type 38 were CDe . Summary/Conclusion: Prevalence of D variant is heterogeneous across different European studies and the results present a new populational profile. The main D variant previously described for the Portuguese population was WD type 2 but our most prevalent D variant was WD type 3. The first study included individuals from Southern and Northern Portugal while this D variant profile analysed only donors from the North. Differences may be associated with regional variations and populational inbreeding due to historical community isolation during past centuries. WD type 38, although a rare variant, is typically associated with Northern Portuguese and Galician individuals. As expected, WD types 1 and 3 were associated with CDe haplotype and WD type 2 was associated with cDE . WD types 1, 2, 3, or 4.0/4.1 do not immunize and can safely be considered RhD positive both as patients and/or pregnant women or as donors. Other WD variants and all partial RhD are considered RhD negative as blood recipients or pregnant women (due to risk of alloimmunization if in contact with an integral RhD protein) although considered as RhD positive while donors (carrying a minor amount of RhD or, at least, a part of RhD protein). WD type 4.2/DAR, WD type 38, and partial D DBT2 blood donors were informed that, although considered RhD positive while donors, they have to be considered as RhD negative if blood recipients or pregnant women and this information was registered on their donor medical file.