Red blood cells are microscopic, disc-shaped cells that circulate throughout the body, transporting oxygen from the lungs to various tissues and organs. This continuous delivery of oxygen is necessary for cellular function and overall health. When red blood cells develop an abnormal shape, it can signal an underlying health issue. Bite cells represent a specific type of damaged red blood cell, indicating an alteration to their membrane. Their presence in a blood sample provides valuable diagnostic clues.
What Are Bite Cells?
Bite cells are red blood cells that exhibit a distinct, irregular shape, appearing as though a portion has been removed from their periphery. They are also known as degmacytes due to this characteristic indentation, resembling a semi-circular “bite” taken out of the cell’s margin. These cells are smaller and denser than normal red blood cells because of the missing fragments.
The appearance of these “bites” can vary, with some cells showing multiple indentations, while others may have a single, smooth concavity. This unique morphology differentiates them from other fragmented red blood cells, such as schistocytes, which are smaller and more irregularly shaped due to mechanical shearing rather than specific removal of cellular components.
How Bite Cells Form
The formation of bite cells begins with oxidative stress inside red blood cells. Oxidative stress occurs when there is an imbalance between the production of reactive oxygen species and the cell’s ability to neutralize them, leading to cellular damage. This stress causes hemoglobin, the oxygen-carrying protein within red blood cells, to denature or unfold from its normal structure.
These denatured hemoglobin molecules then aggregate and precipitate, forming insoluble clumps known as Heinz bodies. Heinz bodies attach to the inner surface of the red blood cell membrane. As these red blood cells circulate, they pass through the spleen, an organ that filters and removes damaged blood cells. Macrophages, specialized immune cells within the spleen, “pit” or remove these Heinz bodies from the red blood cells as they attempt to squeeze through narrow endothelial slits. This mechanical removal of Heinz bodies, along with a portion of the cell membrane, leaves behind the characteristic “bite” or indentation.
Conditions Associated with Bite Cells
The presence of bite cells signals underlying medical conditions that lead to increased oxidative stress or abnormal hemoglobin. One common cause is Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency, a genetic disorder affecting an enzyme that protects red blood cells from oxidative damage. Without sufficient G6PD, red blood cells become vulnerable to damage from oxidative agents, causing hemoglobin to denature and form Heinz bodies. Hemolysis, the premature destruction of red blood cells, results from this oxidative injury.
Unstable hemoglobin variants also lead to bite cell formation. These are inherited disorders where the hemoglobin molecule is prone to denaturing and precipitating within the red blood cell, even under normal conditions or with mild oxidative stress. Drug-induced hemolytic anemia can also cause bite cells, as certain medications, like some antimalarials or sulfa drugs, can induce oxidative stress. Other conditions, such as glutathione synthase deficiency and red cell enzymopathies involving the pentose phosphate shunt, can also contribute to bite cell formation.
Detecting Bite Cells
Identifying bite cells relies on the microscopic examination of a peripheral blood smear. A small blood sample is spread thinly on a glass slide, stained, and viewed under a microscope by a trained professional. This allows for direct visualization of red blood cell morphology, including the distinctive “bitten” appearance.
While a peripheral blood smear is definitive for observing bite cells, other blood tests can provide supportive evidence of red blood cell destruction, known as hemolytic anemia. These tests might reveal a reduced red blood cell count, elevated bilirubin levels (a byproduct of red blood cell breakdown), or increased lactate dehydrogenase (an enzyme released during cell damage). The microscopic assessment remains the direct method for confirming bite cells and aiding in diagnosis.