Hemoglobin S can be separated from hemoglobin D by which method?

• A. Electrophoresis on a different medium and acidic pH
• B. Hemoglobin A2 quantitation
• C. Electrophoresis at higher voltage
• D. Kleihauer-Betke acid elution

Answer: (A)

The key idea is that hemoglobin variants separate by electrophoresis based on their charge, which depends on both the amino acid changes and the pH of the environment as well as the gel medium used. Hemoglobin S and Hemoglobin D have different substitutions in the beta chain, giving them distinct net charges that can be resolved under the right conditions. Running electrophoresis in an acidic medium with a different gel type changes how these charges interact with the gel, producing distinct migration patterns for S and D that you wouldn’t see under standard alkaline conditions. This makes it possible to distinguish S from D by choosing a medium and pH that maximize their separation. The other options don’t achieve this separation: HbA2 quantitation looks at a different Hb fraction and won’t separate S from D; increasing voltage changes speed but not the resolution; and Kleihauer-Betke acid elution is a test for fetal red cells, not for distinguishing Hb variants.