Rouleaux and autoagglutination could be considered forms of poikilocytosis, but differ from the forms discussed previously because groups of cells are involved rather than single cells. In addition, these conditions must be differentiated from similar-appearing artifacts caused by improperly made slides and/or examining morphology in an area that is too thick.
When erythrocytes resemble a toppled stack of coins, the arrangement is referred to as rouleaux. Rouleaux forms when there is an abnormal concentration of plasma protein present in the patient sample, for example, in multiple myeloma. When true rouleaux is present, it can be observed in the optimal smear viewing area at a magnification of 1000X. It is also readily observable at a magnification of 400X. Switching to this lower magnification will help provide confirmation when rouleaux is suspected on a blood smear.