Stomatocytes are a type of red blood cell, or erythrocyte, with an unusual shape. While a healthy red blood cell is a biconcave disc with a circular area of central paleness, a stomatocyte has a central pale area that is elongated and slit-like, resembling a mouth or coffee bean. This form arises from changes to the cell’s membrane. The name “stomatocyte” is derived from the Greek word “stoma,” meaning “mouth,” reflecting this appearance.
Appearance and Identification
The defining feature of a stomatocyte is its morphology on a stained blood sample under a microscope. This gives them a unique appearance often described as resembling a “kissing lip” or “coffee bean.” In three-dimensional space, these cells are not flat discs but are considered overhydrated and bowl-shaped. This structural change is an identifier for laboratory professionals.
Detection of stomatocytes occurs during the microscopic examination of a peripheral blood smear. This procedure involves spreading a thin layer of blood on a glass slide, staining it to make the cells visible, and analyzing the cell populations. A trained medical scientist or pathologist identifies abnormal cell shapes, including stomatocytes, during this review.
The presence of a small number of these cells is not always a cause for concern. They can sometimes appear as “artifacts,” which are changes caused by the preparation or storage of the blood sample rather than a medical condition. The quantity of stomatocytes reported is an important factor in determining their clinical relevance.
Common Causes and Triggers
The appearance of stomatocytes in a blood sample is frequently linked to acquired conditions, with acute alcoholism being a prominent cause. Alcohol can directly affect the lipids in the red blood cell membrane, altering its fluidity and permeability. This disruption leads to the characteristic change in shape.
Liver and gallbladder diseases are also commonly associated with the formation of stomatocytes. In conditions like obstructive liver disease, there can be an increase in the cholesterol content of the red blood cell membrane. This lipid imbalance increases the surface area of the cell, contributing to the morphological changes.
Certain medications are known to induce stomatocyte formation. Drugs that have a cationic, or positively charged, nature can interact with the negatively charged red blood cell membrane. This interaction can cause the cell to swell and take on the classic bowl shape of a stomatocyte. The presence of these cells may be reversible upon discontinuation of the medication.
Associated Genetic Conditions
Beyond acquired causes, stomatocytes are the hallmark of a group of rare genetic disorders collectively known as hereditary stomatocytosis. These conditions are not a single disease but a family of disorders that affect the proteins comprising the red blood cell membrane. The genetic mutations often involve proteins responsible for transporting ions like sodium and potassium across the cell membrane.
A primary consequence of hereditary stomatocytosis is often hemolytic anemia. The abnormal shape and altered membrane properties make the red blood cells fragile and less flexible than normal. As these rigid cells circulate through the narrow passages of the spleen and liver, they are more susceptible to being destroyed, a process called hemolysis.
Hereditary stomatocytosis can be categorized into forms based on cell hydration. In the “overhydrated” form, a defect in ion transport causes water to enter the cell, causing it to swell. Conversely, in the “dehydrated” form, also known as xerocytosis, a different defect leads to a loss of potassium and water from the cell. Both types result in fragile cells, but the specific underlying protein and ion transport defects differ.