New analytical tools and epidemiological data for the identification of HbA2 borderline subjects in the screening for beta-thalassemia

The increase of HbA2 is the most important feature in the identification of beta-thalassemia carriers. However, some carriers are difficult to identify, because the level of HbA2 is not in the typical range. Few data are available concerning the prevalence of such unusual phenotypes, and knowing their expected prevalence could be helpful in detecting systematic drifts in the analytical systems for HbA2 quantification.In this study we report a retrospective investigation in two centres with high prevalence of beta-thalassemia. The prevalence of borderline subjects was found to be 2.2 and 3.0%, respectively. The genotypes of a subgroup of these subjects were then analyzed and in about 25% of cases a mutation in the globin genes was identified. We conclude that the occurrence of HbA2 borderline phenotypes is not a rare event.In order to obtain more accurate HbA2 measurements the development of an international reference measurement system for HbA2, based on quantitative peptide mapping, has been recently started. We believe that the innovative approach of our method could also be used as a model to develop accurate quantitative methods for other red cell proteins relevant to the biodynamic properties and the surface electrochemistry of erythrocytes.