ABO blood grouping may be demonstrated using the 'tile technique'. The serum from blood group A individuals (anti-B), the serum from blood group B individuals (anti-A), and the serum from blood group O individuals (anti-A + B), are reacted with a 3% red cell suspension (made using 3 drops of packed red blood cells mixed with 100 drops of normal saline).The tile is rocked gently allowing the serum and the red cell suspension to mix. Clumping (agglutination) of the cells occurs where there is an antibody spe cific for the antigens on the red cells. Where there is no antibody-antigen reaction the red cells remain in suspension. The reaction pattern for each of the ABO groups is shown in below table.