Wright's Stain, 500x

Rouleaux in a feline blood smear

The observation of rouleaux must be distinguished from the  agglutination of red blood cells. The formation of rouleaux consists of the piling of erythrocytes and is a physiological phenomenon linked to plasma proteins. It is more common in certain species (ex: cat, horse). Agglutination is due to the presence of antibodies on the surface of the erythrocytes which joins them together ( not all antibodies result in this reaction). Agglutination may be observed in cases of immune-mediated hemolytic anemia, and also during cryoglobulinemia (a rare condition).