An assaying kit is for pre-transfusion blood group matching between two blood samples. The kit includes at least two assemblies (101,201) corresponding to the first and the second blood sample, each assembly has at least two test units (1). Each test unit (1) includes a reagent containing an antigen present on erythrocytes or an antibody able to bind to an antigen present on erythrocytes. Each test unit (1) also includes a membrane (2) permeable to free erythrocytes (6) and impermeable to hemagglutinated erythrocytes. The antibody contained in the first test unit for both the first assembly (101) and the second assembly (201) corresponds to a first blood group and the antibody contained in the second test units for both the first assembly (101) and the second assembly (201) corresponds to a second blood group.