In haematology, red cell agglutination is the process whereby red cells clump together forming aggregates. This is seen in Waldenström's macroglobulinemia, cold agglutinin disease and Infection with Mycoplasma Pneumonia. In haematology, red cell agglutination is the process whereby red cells clump together forming aggregates. This is seen in Waldenström's macroglobulinemia, cold agglutinin disease and Infection with Mycoplasma Pneumonia.