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Diagnostic Tests: Fragmented Red Blood Cells (Schistocytes)
Overview — What This Is
The smear shows fragmented red blood cells, also referred to as schistocytes or helmet cells. These irregularly shaped RBC fragments form when erythrocytes are mechanically sheared within the circulation. Their presence is a hallmark of intravascular hemolysis and defines microangiopathic hemolytic anemia (MAHA).
Diseases Associated With Schistocytes
Fragmented RBCs occur in conditions where red cells are destroyed while passing through areas of fibrin deposition, turbulence, or mechanical injury. Major associated disorders include:
- Thrombotic Thrombocytopenic Purpura (TTP)
- Hemolytic Uremic Syndrome (HUS)
- Disseminated Intravascular Coagulation (DIC)
- Major blood group incompatibility (e.g., ABO mismatch)
- Paroxysmal Nocturnal Hemoglobinuria (PNH)
- Mechanical destruction from:
- Artificial heart valves
- Mechanical circulatory support devices (e.g., LVADs)
- Snake bites (due to hemotoxic venom effects)
These conditions share a common mechanism—red cell fragmentation within the vascular system.
Associated Laboratory Abnormalities
Because schistocytes signify intravascular hemolysis, several classic lab abnormalities accompany their presence:
- Elevated LDH — released from destroyed RBCs
- Elevated indirect (unconjugated) bilirubin — from heme breakdown
- Elevated reticulocyte count — bone marrow compensation
- Decreased haptoglobin — binds free hemoglobin, becomes depleted in intravascular hemolysis
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