Echinocytes in freshly-collected blood from a horse with colic. Echinocytes are spiculated RBCs. The term crenation is also used to refer to cells of this type. The projections of the cell membrane may be sharp or blunt, are usually numerous, and tend to be evenly spaced around the circumference. Spicules are usually of uniform size which differentiates echinocytes from acanthocytes which have irregularly sized spicules, irregularly spaced around the cell membrane. Causes of echinocyte formation Artifact: Echinocytes usually represent an in vitro artifactive change, resulting from aging of the blood (decreased ATP) and/or exposure to excessive concentrations of EDTA as occurs when the sample tube is significantly underfilled (dehydrates the red blood cells). Echinocyte formation occurs because of red cell dehydration, increased pH and decreased ATP. Drugs: Drugs that expand the outer leaflet of the red blood cell membrane produce echinocytosis, e.g. salicylates, phenylbutazone, calcium, furosemide, chemotherapeutic agents (e.g. doxorubicin). Horses: When seen in fresh, well-handled blood, echinocytes usually indicate whole body electrolyte depletion. Reduction in intracellular erythrocyte K+ causes red cell dehydration and echinocyte formation. This occurs commonly in horses with electrolyte depletion from sweating (endurance horses) or diarrhea (gastrointestinal disturbances such as colitis). Low sodium is the most common electrolyte abnormality seen in blood samples from horses with echinocyte formation. (Remember that blood K+ is not a reflection of total body potassium levels.) Rattlesnake envenomation can also produce echinocytosis and is a useful blood marker for this disorder. Dogs: Non-artifactual echinocytes are observed in dogs with renal disease (especially glomerulonephritis), pyruvate kinase deficiency (spheroechinocytes), rattlesnake and coral snake envenomation (phospholipases in the venom alter red cell membrane phospholipids) and neoplasia (where it may be secondary to chemotherapeutic agents).