Destruction of red cells (hemolysis) may be intravascular (within blood vessels) or extravascular (outside of blood vessels). Complement causes intravascular hemolysis, which can lead to hemoglobinemia (free hemoglobin in the serum/plasma) and hemoglobinuria (free hemoglobin in the urine). Phagocytosis of red cells by macrophages facilitates extravascular hemolysis, which causes increase in serum bilirubin.
Potential serological/laboratory findings encountered when an immune-mediated anemia is present include:
- Decreased hemoglobin and hematocrit
- Possible compensatory increase in nucleated red blood cells
- Elevated bilirubin and lactate dehydrogenase (LDH) levels
- Decreased haptoglobin
- Positive DAT due to IgG and/or complement sensitization
- Positive antibody screen