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Stomatocytes

Stomatocytes are erythrocytes with a slit-like central pallor, giving them the appearance of "coffee beans" or "kissing lips." In three dimensions, the stomatocyte is actually the shape of a bowl, as the cell has lost its biconcave morphology due to a membrane defect. Most cases of stomatocytosis are due to alteration in permeability, leading to an increase in red cell volume. Stomatocytes form at a low blood acidic pH, as seen in exposure to cationic detergents and in patients receiving phenolthiazine or chlorpromazine. Stomatocytosis can be an inherited or acquired condition.
In hereditary stomatocytosis, mild anemia and findings of on-going hemolysis may be evident if the condition presents as a clinical problem at all. Individuals who possess the Rh null phenotype have osmotically fragile red cells, which take the form of stomatocytes. Individuals with this phenotype tend to experience varying degrees of chronic hemolytic anemia.
Note: Unless 10% or more of the RBC's are stomatocytes, their presence is probably artifactual.