Hb Bart's immunochromatographic test result and Hb F level in normal cord blood and in selected haemoglobinopathy cases

Abstract

Hb Bart's immunochromatographic strip test for alpha thalassaemia detection (AT-ICT) uses monoclonal antibody to detect the raised Hb Bart's present in the peripheral blood of persons with alpha thalassaemia conditions. The test was developed in 2009 and subsequently marketed for clinical laboratory use (iLab alpha-thal™, i + Med Laboratories, Bangkok, Thailand). 1 Due to its increased sensitivity and specificity, ease of use, and reduced cost, clinical laboratories are increasingly using the AT-ICT in the haemoglobinopathy testing. False positive results, however, are observed in conditions associated with high Hb F level including newborn babies and delta-beta thalassaemia carriers. 2 Occasional false positive results have also been reported in other haemoglobinopathy disorders, including Hb E and beta thalassaemia conditions. 3,4 There is no published study correlating the false positive AT-ICT result with Hb F level. The package insert indicates the test is unsuitable for cord blood or newborn samples, but there is no advice on the age when the test can start to be used for alpha thalassaemia detection. The false positive result cannot be attributed to cross-reaction with Hb F as the anti-Hb Bart's antibody does not cross-react with purified Hb F and Hb A. 1 The cause of the false positivity and its relationship to the alpha/non-alpha globin synthesis ratio in the red cells therefore remain unknown.We correlated the Hb F levels with AT-ICT results when there is no globin chain abnormality involved by using dilutions of normal cord blood in normal adult blood. We also reviewed the AT-ICT results in selected cases of haemoglobinopathy with elevated Hb F. These were