[Mistyping of ABO grouping by polyagglutination]

Polyagglutination is a phenomenon that a sample of patient's red blood cells is agglutinated by most of normal human sera. In patients with bacterial infection or hematological diseases, red cells may become agglutinable due to an exposure of antigens (cryptoantigen) that are usually hidden as submembrane structures of normal red cells. Most of normal sera contain natural antibodies to the corresponding antigens. Polyagglutination can cause apparent discrepancies between ABO antigen and antibody tests with the patient's sample, resulting in mistyping of ABO grouping. In some cases, polyagglutination is observed only by the minor test of cross-matching without showing the discrepancies. Recently polyagglutination has been rarely seen probably because of increasing use of monoclonal antibodies and dispensing minor test for cross-matching. Because no obvious case of adverse reaction by polyagglutination through transfusion is recently reported, clinical significance of polyagglutination seems extremely low.