Nonspecific agglutination of red cells in the presence of human serum, not related to blood group specificity. This occurs most often as a consequence of infections, when bacterial enzymes actually strip off parts of antigens normally present of the surface of the red cell. This action exposes antigens that are normally hidden, called “cryptantigens.” Most everyone has IgM antibodies that react against these cryptantigens, but since the antigens are not usually exposed, the antibodies don’t cause a problem. T activation is the most common type of polyagglutination. By definition, acquired polyagglutination is transient, and effective treatment of the infection eliminates the nonspecific agglutination. Inherited forms occur, however (including Tn polyagglutination and HEMPAS), and some forms that we just don’t understand yet. The different forms of polyagglutination are generally distinguished by the use of a panel of various lectins. The thing that confuses people most often about this entity is that it is primarily a red cell issue, not a plasma issue.