Haptoglobin is the plasma protein responsible for binding free hemoglobin during episodes of hemolysis. Because of its role, haptoglobin typically decreases levels during a hemolytic crisis since free hemoglobin is spilled into the bloodstream from lysed red blood cells.
The average level of haptoglobin is 40–330mg/dL. Individuals in hemolytic crisis demonstrate significantly reduced levels to a complete absence of haptoglobin.
However, haptoglobin levels in alpha thalassemia remain normal or only slightly decreased, even during hemolytic events.
This is because haptoglobin functions by binding the alpha chain portion of hemoglobin. With the absence of these chains in alpha thalassemia major and intermedia, haptoglobin cannot bind free hemoglobin. Therefore, it is not consumed as it would be in other types of hemolytic anemia.
