Hematology Case 44

• Suggested Redding:

((( Beyond the neonatal period, compound heterozygosity for β^S and β⁰ thalassaemia can often be distinguished from β^S homozygosity on HPLC by an increased percentage of haemoglobin A 2 , reported values being usually 4 – 5.6% for S β⁰ thalassaemia in comparison with 1.6 – 3.6% for SS. However it should be noted that there is some overlap in A2 percentages, particularly when co - inheritance of α thalassaemia raises the A2 percentage in β^S homozygotes. There is also overlap in haemoglobin F levels, which are usually 5 – 15% in compound heterozygotes. If the red cell indices are normal, β^S β⁰ thalassaemia can be excluded, but in patients with microcytosis the differential diagnosis is between β^S β^S with coexisting α thalassaemia and β^S β⁰ thalassaemia. When a precise diagnosis is important, e.g. for genetic counselling, either family studies or DNA analysis can permit a distinction. Compound heterozygotes for β^S and β⁺ thalassaemia are readily recognized by all techniques because of the presence of haemoglobin A))), Barbra J. Bain, et al, Variant Haemoglobins - A giude to identification, 2010, P 37.