Rouleaux formation is most commonly observed in which species based on routine blood smears?

Rouleaux formation is most commonly observed in which species based on routine blood smears?

• A. Rats
• B. Dogs
• C. Horses
• D. Pigs

Answer: (C)

Rouleaux formation is when red blood cells line up in stacked, coin-like columns because plasma proteins such as fibrinogen and globulins reduce the surface charge that normally keeps cells from sticking together. This stacking is particularly common in horses on routine blood smears, so it’s a classic observation in that species. In other animals, rouleaux can occur but is less typical and often reflects a higher level of plasma proteins due to inflammation or other hyperproteinemic states. A handy note is that rouleaux dissolve with saline dilution, helping distinguish it from true agglutination, which remains clumped.

Rouleaux formation is when red blood cells line up in stacked, coin-like columns because plasma proteins such as fibrinogen and globulins reduce the surface charge that normally keeps cells from sticking together. This stacking is particularly common in horses on routine blood smears, so it’s a classic observation in that species. In other animals, rouleaux can occur but is less typical and often reflects a higher level of plasma proteins due to inflammation or other hyperproteinemic states. A handy note is that rouleaux dissolve with saline dilution, helping distinguish it from true agglutination, which remains clumped.