Effect of megaloblastic anemia on hemoglobin A₂ and diagnosis of β-thalassemia trait

β-thalassemia trait is usually diagnosed by raised hemoglobin A₂ (HbA₂). The presence of megaloblastic anemia can cause an increase in HbA₂ and create a diagnostic dilemma. Here, we have analyzed the effect of vitamin B12 and folic acid supplementation on HbA₂ and diagnosis of β-thalassemia trait in cases of megaloblastic anemia with raised HbA₂.

Cases of megaloblastic anemia with raised HbA₂ on high-performance liquid chromatography (HPLC) were supplemented with vitamin B12 and folic acid. Post-treatment evaluation was done after 2 months. Cases showing adequate hematological response were subjected to statistical analysis. Based on post-treatment HbA₂ value, the cases were diagnosed as normal, borderline raised HbA₂, or β-thalassemia trait. Pre- and post-treatment values of red cell parameters and HbA₂ were analyzed.

There was a significant decrease in HbA₂ value after vitamin B12 and folic acid supplementation. The diagnosis was changed in 70.97% of the cases after treatment. The chance of inconclusive diagnosis was decreased from more than 50% to less than 10%. Pre-treatment mean corpuscular volume (MCV) and HbA₂% showed a significant difference between the thalassemic and normal groups.

Megaloblastic anemia can lead to false-positive diagnosis of β-thalassemia trait on HPLC. Repeat HPLC should be done after adequate supplementation of vitamin B12 and folic acid in cases of megaloblastic anemia with raised HbA₂. Red cell parameters are not helpful to suspect β-thalassemia trait in presence of megaloblastic anemia. However, HbA₂% on HPLC can be a useful parameter to suspect or exclude β-thalassemia trait in cases of megaloblastic anemia.