Is Estimation of HbA2 Alone Sufficient for Screening Beta Thalassaemia Carriers: A Case in Perspective

Beta thalassaemia is one of the most common inherited haemoglobinopathies, characterised by reduced or absent production of the beta globin chain. In India, the carrier frequency of thalassaemia is estimated to be 3-4%. The prevention of Beta thalassaemia is the best strategy, and this can be achieved through carrier screening and prenatal diagnosis. Carriers of beta thalassaemia can be easily identified using haematological parameters such as complete blood count and High Performance Liquid Chromatography (HPLC) for haemoglobin analysis. The characteristic findings observed in thalassaemia carriers include microcytosis, hypochromia, with a Mean Corpuscular Volume (MCV) of less than 80 fL and Mean Corpuscular Haemoglobin (MCH) of less than 28 pg. They also present with elevated levels of HBA2 (α2δ2) ≥3.5%. Carrier screening for beta thalassaemia primarily relies on the observation of elevated HbA2 levels. However, in rare cases, some carriers can have normal HbA2 levels, leading to false-negative screening results. In a case involving a married couple who underwent routine preconceptional screening by complete blood count and HPLC for thalassaemia screening, the male partner had elevated HbA2 levels (5.2%), while the female partner had normal HbA2 levels (1.6%). Molecular testing revealed that the male partner was heterozygous for the Intervening Sequence (IVS) 1-5 (G>C) mutation, while the female partner was found to be heterozygous for the CD41-42 (-CTTT) mutation. It is important to consider molecular testing of the HBB gene in couples, even if one partner is a carrier and the other partner has normal or borderline HbA2 levels.