Haemoglobin A2' and its significance in beta thalassaemia diagnosis

We have studied, haemoglobin A(2)' (A(2) prime), a delta chain variant haemoglobin occurring in a small percentage of individuals of African ancestry. In heterozygotes, the percentage of haemoglobin A(2)' was found to be slightly lower then the percentage of haemoglobin A(2), suggesting that the variant delta chain is synthesized at a reduced rate. When quantifying haemoglobin A(2) for the diagnosis of beta thalassaemia heterozygosity, it is essential to add together the A(2) and A(2)' to give 'total haemoglobin A(2)'. However, it not necessary to use a different reference range for total haemoglobin A(2) in A(2)' heterozygotes. When using microcolumn chromatography, A(2)' was found to be measured with A(2). On the high-performance liquid chromatography instrument studied, haemoglobin A(2)' fell in the haemoglobin S window but its retention time differed from that of haemoglobin S.