A patient of Southeast Asian heritage presents with mild microcytic anemia and target cells. Hemoglobin electrophoresis on cellulose acetate at pH 8.4 shows a major band that migrates with Hb A2 and no Hb A, and citrate agar electrophoresis shows the band in the position of Hb A. Which abnormal hemoglobin is most probable?

• A. Hb E
• B. Hb A
• C. Hb C
• D. Hb D

Answer: (A)

This pattern hinges on how electrophoresis separates hemoglobins by their net charge, which can change with a specific mutation. The beta-globin mutation in Hb E alters the molecule’s charge so it moves differently depending on the buffer used.

On alkaline cellulose acetate (pH around 8.4), the abnormal Hb E migrates together with Hb A2, while Hb A is absent. That tells you the major hemoglobin present is not Hb A and has the same mobility as Hb A2 under alkaline conditions. On citrate agar (an acidic medium), the same band shifts to the position of Hb A. This dual mobility is characteristic of Hb E: its charge causes it to co-migrate with Hb A2 in alkaline gel but resemble Hb A on acidic gel.

In a patient from Southeast Asia with mild microcytic anemia and target cells, this combination is classic for Hb E, especially when Hb A is absent or greatly reduced, consistent with Hb E disease (homozygous Hb E). The other variants do not produce this exact pattern of migration across the two gel systems, so the most probable abnormal hemoglobin is Hb E.