Numerous stomatocytes in the blood of a chondrodysplastic Alaskan malamute dog.
Stomatocytes are erythrocytes with an elongated (mouth-like) area of central pallor. An occasional cell of this type might be seen as a non-specific finding in a variety of situations, such as regenerative anemias, liver disease, and lead poisoning. Stomatocytes can also be an artifact in a blood smear that is too thick.

Hereditary stomatocytosis occurs in some Alaskan Malamute dogs in association with chondrodysplasia which manifests as dwarfism. It is inherited as an autosomal recessive trait. In addition to the morphologic abnormality, the red cell population in homozygous affected dogs is macrocytic (up to 98 fL), and hypochromic (26-28%). Erythrocyte numbers are lower than normal, but, due to the larger cell size, hematocrits are within reference intervals. Red blood cell lifespan is reduced, with extravascular hemolysis and a mild reticulocytosis, and the cells are osmotically and mechanically fragile. The precise defect is unknown, but it is a membrane defect involving increased sodium and water influx. Hereditary stomatocytosis has also been reported in Drentse patrijshond (in conjuction with hypertrophic gastritis) and Miniature Schnauzers (autosomal recessive). We have seen one case of stomatocytosis in a Peek-a-poo at Cornell University. In the Drentse patrijshond, dogs are anemic (Hct, 18-38%) with reticulocytosis (2.4-12%), macrocytic (72-81 fL) and hypochromic. Stomatocytes are seen in 14-38% of red blood cells by light microscopy. The defect is due to abnormal phospholipid composition in the red blood cell membrane (increased sphingomyelin and decreased cholesterol and phosphatidylcholine, with the latter being the most consistent change). The dogs usually die of hemolytic anemia.