This photo shows crenated red cells, also known as echinocytes or burr cells. Crenated
red cells have changed from a disc shape to spheres covered with short, sharply pointed
Slow drying of the smear and aging of blood in the tube are the most common causes of artifactual crenation. Older red cells, whether aged in circulation or in the tube, are more prone to undergo the discocyte-echinocyte transformation than younger red cells. You can see crenated red cells in the thick part of any blood smear. Echinocytes in the good-for- examination area of a well-made smear of fresh blood are not artifacts of preparation but an abnormality of red cell shape that is non-specific with regard to cause.
Non-artifactual echinocytes in horses are thought to be secondary to electrolyte imbalances, especially hyponatremia. Echinocytes are more numerous in sick dogs and cats, regardless of specific disease, than in healthy animals. Echinocytes often are not reported, since they are artifacts in many cases and a non-specific abnormality in others and it is often difficult to distinguish "real" from artifactual echinocytes.