Unlike rouleaux formation, in which erythrocytes lie in rows, in agglutination, the erythrocytes arrange themselves in amorphous associations. This phenomenon can be observed in the occurrence of cold agglutinins. If the blood is warmed to 37°C before examination agglutination disappears. Also the often observed elevated MCHC in automated cell counters goes away after worming of the blood.
Autoimmune hemolytic anemia with cold-reactive anti-erythrocytic autoantibodies.