Which of the following is NOT associated with sideroblastic anemia?

Sideroblastic anemia is characterized by the body's inability to properly incorporate iron into hemoglobin, leading to the accumulation of iron in the mitochondria of erythroblasts, which can be seen as ringed sideroblasts on bone marrow examination.

The presence of increased serum iron is common in this condition due to the ineffective erythropoiesis associated with sideroblastic anemia, which leads to iron overload. Ringed sideroblasts, the hallmark of the condition, specifically indicate the abnormal iron metabolism in the bone marrow. A dimorphic blood picture may also be observed, reflecting a combination of microcytic and macrocytic red blood cells in the peripheral blood due to the underlying erythropoietic abnormalities.

In contrast, increased RBC protoporphyrin is not typically associated with sideroblastic anemia. In fact, patients with sideroblastic anemia often show decreased levels of protoporphyrin due to the impairment in iron utilization, leading to defective heme synthesis. Therefore, the correct answer indicates a fundamental aspect that distinguishes this type of anemia from the others typically observed in conjunction with it.