RhD antigen is the main antigen of the Rh system and belongs to the clinically most relevant antigens of the human red cell. Correct determination of the RhD status is important for the prevention of haemolytic transfusion reactions and for prevention and treatment of the haemolytic disease of the newborn. Numerous atypical forms of RhD protein (D variants = qualitative changes; weak D = quantitative changes) complicate RhD assessment. Knowledge of the frequency of variant and weak D types in the population is helpful for the choice of optimal anti-D reagents and for transfusion and immunoprophylactic recommendations. The authors present the first extensive study of atypical D antigens in the Czech population.Most frequent variants detected were D VI (10x), DFR (7x) and D VII (6x), relatively frequent (3x) was DCS variant, which was so far detected only in the local population. In our study we detected also DIVb and rare variants DOL and DYO. Alloimmunization was detected in patients with variants D IIIc, D VII and DNB. In carriers atypical D antigen in Rh phenotype R1r the frequency of D variants was cca 7% while in Rh phenotype R2r was five times more frequent – Rh phenotype could serve as a guide for safer substitution and prophylaxis before definitive assessment of the D weak or variant type. Possibilities and limits of use of commercial kits for D pheno- and genotyping in the Czech population are discussed.

        Key words: RhD antigen, variant D antigens, weak D antigens, frequency, detection by monoclonal antibodies and PCR-SSP