Rouleaux (singular is rouleau) are stacks or aggregations of red blood cells (RBCs) that form because of the unique discoid shape of the cells in vertebrates. The flat surface of the discoid RBCs gives them a large surface area to make contact with and stick to each other; thus forming a rouleau.

What causes rouleaux formation?

The appearance of rouleaux may be artificially caused by a poor preparation of the smear or by viewing the slide in a thickened area. When rouleaux formation is truly present, it is caused by an increase in cathodal proteins, such as immunoglobulins and fibrinogen.

What causes rouleaux formation in agglutination?

Rouleaux formation

Horse red blood cells are thought to form rouleaux because they have decreased negative charge (altered zeta potential) on their red blood cells.