Which test differentiates Hb S trait from other variants when solubility results are inconclusive?

Which test differentiates Hb S trait from other variants when solubility results are inconclusive?

• A. Citrate agar electrophoresis at pH 6.2
• B. HbA2 quantitation
• C. Acid elution stain
• D. Blood film evaluation

Answer: (A)

When a solubility test isn’t clear, you need a method that separates hemoglobins by how they move in a charged medium. Citrate agar electrophoresis at pH 6.2 does exactly that, because the acidic environment gives Hb variants different mobilities. Hb S behaves distinctly from Hb A and other variants at this pH, producing a characteristic pattern that lets you confirm Hb S trait versus other variants. In Hb S trait, you typically see both Hb A and Hb S bands, whereas other variants show a different banding pattern, providing a definitive distinction when solubility alone isn’t conclusive. HbA2 quantitation isn’t used to identify Hb variants; it reflects an abnormal HbA2 level primarily for thalassemia assessment. Acid elution stain is a screening method with less definitive discrimination between variants. Blood film evaluation can reveal cell morphology but cannot reliably differentiate specific hemoglobin variants.

When a solubility test isn’t clear, you need a method that separates hemoglobins by how they move in a charged medium. Citrate agar electrophoresis at pH 6.2 does exactly that, because the acidic environment gives Hb variants different mobilities. Hb S behaves distinctly from Hb A and other variants at this pH, producing a characteristic pattern that lets you confirm Hb S trait versus other variants. In Hb S trait, you typically see both Hb A and Hb S bands, whereas other variants show a different banding pattern, providing a definitive distinction when solubility alone isn’t conclusive.

HbA2 quantitation isn’t used to identify Hb variants; it reflects an abnormal HbA2 level primarily for thalassemia assessment. Acid elution stain is a screening method with less definitive discrimination between variants. Blood film evaluation can reveal cell morphology but cannot reliably differentiate specific hemoglobin variants.