Flexi Says: Blood type is determined using agglutination reaction of antibodies to test the type of antigens present on the RBCs of the subject. The blood sample is observed after mixing it with anti-A and anti-B antibodies. If the blood type is A it will react only with anti-A antibodies and the RBCs will show clumping. The same goes for B. If both antibodies react, the type will be AB, and if none of the antibodies react the blood type will be O. The Rhesus factor is also tested using anti-Rh antibodies and then the blood type of the person is determined as Rh+ve or -ve.