What are the Histological Features of Hemoglobin Bart's?

Histologically, Hb Bart's can be identified by examining erythrocytes in a blood smear. The erythrocytes may appear hypochromic (pale due to reduced hemoglobin content) and microcytic (smaller than normal). In more severe cases, such as Hb Bart's hydrops fetalis, there is extensive extramedullary hematopoiesis, which can be observed in the liver and spleen. Here, histological examination may reveal an increase in immature erythroid precursor cells as the body attempts to compensate for the ineffective erythropoiesis.