Which statement correctly differentiates sickle cell trait from S/B+ thalassemia?

Which statement correctly differentiates sickle cell trait from S/B+ thalassemia?

• A. Trait has more HbS and less HbA
• B. Trait has less HbS and more HbA
• C. Thalassemia leads to macrocytosis
• D. Trait lacks HbA2

Answer: (B)

Discrimination between sickle cell trait and S/B+ thalassemia hinges on the balance of HbA and HbS in red cells. In sickle cell trait you have one normal beta-globin gene and one sickle gene, so HbA remains the majority while HbS is present at a lower but meaningful level. In beta+ thalassemia coexisting with the S gene, beta-globin synthesis is reduced, so HbA production falls and HbS makes up a larger fraction of total hemoglobin. That makes the statement that trait has less HbS and more HbA the best distinction. The other options don’t fit: trait does not have more HbS than HbA; macrocytosis is not the defining differentiator here; and HbA2 is present at normal levels in sickle trait (it’s typically elevated only in beta-thalassemia trait).

Discrimination between sickle cell trait and S/B+ thalassemia hinges on the balance of HbA and HbS in red cells. In sickle cell trait you have one normal beta-globin gene and one sickle gene, so HbA remains the majority while HbS is present at a lower but meaningful level. In beta+ thalassemia coexisting with the S gene, beta-globin synthesis is reduced, so HbA production falls and HbS makes up a larger fraction of total hemoglobin. That makes the statement that trait has less HbS and more HbA the best distinction. The other options don’t fit: trait does not have more HbS than HbA; macrocytosis is not the defining differentiator here; and HbA2 is present at normal levels in sickle trait (it’s typically elevated only in beta-thalassemia trait).