 Heterophile also can mean that it is an antibody that reacts with antigens other than the antigen that stimulated it (an antibody that crossreacts).A 20% suspension of horse red cells is used in an isotonic 3–8% sodium citrate formulation.One drop of the patient's serum to be tested is mixed on an opal glass slide with one drop of a particulate suspension of guinea-pig kidney stroma, and a suspension of ox red cell stroma; sera and suspensions are mixed with a wooden applicator 10 times.