The ICT is simple to perform, with higher sensitivity than HbH-i, and gives the result in a short time and at a lower cost. This can be used by clinical laboratories to replace HbH-i for α-thalassaemia detection.

Alpha thalassaemia mutations are common, with around 0.3% of the world population carrying an alpha-zero thalassaemia mutation, and 27% carrying an alpha-plus thalassaemia mutation. 1 The alpha thalassaemia genotype is clinically important as it can lead to congenital anaemias or modify the clinical severity of other significant haemoglobinopathies including beta thalassaemia and sickle cell disease. 2 Hb Bart's immunochromatographic strip test for alpha thalassaemia detection (AT-ICT) was introduced in 2009, and is being used increasingly by clinical haematology laboratories for haemoglobinopathy study.The AT-ICT uses purified anti-Hb Bart's antibody to detect the raised Hb Bart's in the peripheral blood of alpha thalassaemia carriers. 3 Compared to the conventional red cell Hb H-inclusion test commonly used in phenotypic haemoglobinopathy testing, AT-ICT has improved overall sensitivity of 63%-76% (alpha-zero 97%-100%, alpha-plus 44%-70%) and specificity of 91%-100% for alpha thalassaemia detection. [4][5][6] It has the advantages of fast turnaround time, requiring no special equipment or technical expertise and lower operator cost.The AT-ICT results, however, can be falsely positive in newborn babies when the Hb F levels are high. 5 Occasional false positive results have also been reported in other haemoglobinopathy conditions, mainly in Hb E, Hb S and beta thalassaemia conditions. 4,6

We report here a patient heterozygous for a previously unreported β chain variant. A 72-year-old Caucasian female was found to have an abnormal hemoglobin (Hb) as an incidental finding following Hb A1C analysis. There was no family history of anemia or hemoglobinopathy. Her full blood count revealed a mild normochromic anemia with Hb 11.1 g/dL (range 11.5-15.0), mean corpuscular volume (MCV) 93.0 fL (range 80.0-100.0) and mean corpuscular Hb (MCH) 30.0 pg (range 27.0-32.0). Isopropanol stability tests and a variant Hb on high performance liquid chromatography (HPLC) comprizing 37.0% of the total Hb suggested an unstable Hb variant. Sanger sequencing of the β-globin gene revealed a single base substitution, HBB: c.37A>C, causing the missense mutation β12(A9)Thr → Pro in exon 1 of the HBB gene. This mutation changes the threonine residue at position 12(A9) to a proline in the β-globin chain. We propose that this variant be called Hb Feilding after the town where the proband lived. Three dimensional modeling suggested that the disruption of the Hb structure was due to the introduction of a proline at helix A9 which caused distortion of the helical structure and resulted in reduced solubility.

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