Depiction of a forward type (A), reverse type (B), and mixed field agglutination in a type A patient (C). When the anti-A reagent is added, it causes the patient’s group A erythrocytes to agglutinate, whereas adding anti-B reagent does not cause the patient’s group A erythrocytes to agglutinate. When group O erythrocytes are transfused to the group A recipient and anti-A reagent is added, the patient’s group A erythrocytes agglutinate, but the transfused group O erythrocytes do not agglutinate, thereby creating a mixed field appearance. RBC, erythrocyte (red blood cell).