HbA₂ Measurements in β-Thalassemia and in Other Conditions

Quite a few papers have been written on the significance of elevated hemoglobin (Hb) A₂ as a parameter for the diagnosis of β-thalassemia trait, on the cutoff values to be used in diagnostics and on the significance and effects of factors reducing or elevating the expression of HbA₂ and last but not least on the need for reliable measurement methods and precise calibrations with accurate standards. However, little has been published on the causes that elevate or reduce the HbA₂ levels in β- and a-thalassemia and in other conditions. For a better understanding of the value of a precise measurement of this parameter we summarize and elucidate in this review the direct and indirect mechanisms that cause the variations in HbA₂ expression and that influence the value of this parameter in particular conditions. We conclude by explaining the advantages and disadvantages of trusting on a precise measurement in the complete diagnostic contest.