Echinocyte comes from the Greek word meaning "sea urchin," which relates to its shell-like appearance. Echinocytes, more commonly referred to as burr cells, are reversible, meaning that this alteration can be the result of the cell's environment, pH of the medium (including the glass slides on which blood smears are made), the metabolic state of the cell and the use of some chemical substances. Several echinocytes (burr cells) can be seen in the top image; three of them are indicated by the arrows. Notice that the projections are rounded and evenly spaced around the cell and the cells have central pallor. Acanthocytes, by contrast, have irregularly spaced thorn-like projections and little or no central pallor.
Although burr cells may be associated with diseases, such as uremia or pyruvate kinase deficiency, crenated cells, that may be confused with true burr cells/echinocytes, are frequent artifacts. Crenated erythrocytes are most commonly caused by excess EDTA (underfilled collection tube), but may also be caused by slow drying, drying in a humid environment, or an alkaline pH from glass slides. When crenation is an artifact, most cells on the slide will exhibit this characteristic. True burr cells are less numerous. Corrective actions include making a new smear or re-collecting the sample, if possible. The bottom image contains crenated cells that were the result of an underfilled EDTA collection tube. These should not be reported.