Echinocytes cells are erythrocytes with multiple protrusions due to disruption of the cell membrane. Formally, a distinction is made between echinocytes (10-30 regular protrusions) and acanthocytes (<20 irregular, pointed protrusions), but this is often very difficult in practice. However, their etiology is different.

Acanthocytes arise from increased uptake of cholesterol into the membrane, which can be seen in disturbed lipid metabolism. Echinocytes can arise from too slow drying of a blood smear, prolonged exposure to EDTA (artefact) or from physiological disruption of the osmotic gradient (and thus relative dehydration of the erythrocyte).