Haptoglobin is the plasma protein responsible for binding free hemoglobin during episodes of hemolysis and would normally demonstrate decreased levels during a hemolytic crisis.

The normal level of haptoglobin is 40-330mg/dl. Individuals who are in hemolytic crisis demonstrate greatly reduced levels to an absence of haptoglobin.

In alpha thalassemia, however, haptoglobin levels remain normal or only slightly decreased, even during hemolytic events.

The reason for this is that 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.