False positive Hb Bart's immunochromatographic strip test for alpha thalassaemia in delta‐beta thalassaemia carriers

Abstract

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