Question of the Day

This is red blood cell (RBC) stacking, a.k.a. rouleaux formation, on a feline blood smear; this is a normal finding in cats and horses.

Always differentiate normal rouleaux formation from RBC agglutination, which is not normal. 

Here is more useful information from Cornell’s eClinPath website about RBC agglutination and rouleaux formation).

Here is equine rouleaux formation (note the characteristic equine eosinophil at the top).

Remember, normal goats may have marked poikilocytosis; camelids have ellipsoid RBC; and normal RBCs in birds and reptiles are nucleated.

Image courtesy of Dr. Seth Chapman.