Which type of anemia is associated with an increase in indirect bilirubin?

Hemolytic anemia is characterized by the premature destruction of red blood cells, which leads to the release of hemoglobin from these cells into the bloodstream. When hemoglobin is released, it is further broken down into heme and subsequently degraded into bilirubin. Indirect (unconjugated) bilirubin arises from the breakdown of heme, and an increase in hemolysis results in elevated levels of indirect bilirubin in the blood.

In hemolytic anemia, because red blood cell destruction occurs at a higher rate than the liver can conjugate this bilirubin for excretion, there is a resultant increase in indirect bilirubin levels. This is a hallmark of hemolytic processes.

In contrast, other types of anemia, such as iron deficiency anemia, aplastic anemia, and anemia of chronic disease, do not typically involve significant hemolysis of red blood cells. These anemias are related to factors such as reduced production of red blood cells or iron deficiency rather than increased destruction, hence they do not cause a rise in indirect bilirubin. This physiological mechanism highlights why hemolytic anemia is specifically linked to increased levels of indirect bilirubin.