Routine screening for α-thalassaemia using an immunochromatographic strip assay for haemoglobin Bart's

Abstract

Objective: To evaluate an immunochromatographic (IC) strip assay for Hb Bart's as a routine screening test for a-thalassaemia in area with a high prevalence of thalassaemia and haemoglobinopathies. Methods: A total of 300 adult screen positive blood specimens were collected at an ongoing thalassaemia screening programme in northeast Thailand. Routine screening was done using red blood cell indices, osmotic fragility, and dichlorophenolindophenol tests. The IC strip assay for haemoglobin Bart's was performed on all samples. The result was evaluated against thalassaemia genotypes determined using standard haemoglobin and DNA analyses. Results: Of 300 subjects investigated, Hb and DNA analyses identified 32 with normal genotype. The remaining subjects carried thalassaemia with as many as 16 different genotypes. Hb Bart's was detected in all cases, with several a 0 -thalassaemia (SEA type) related disorders. Of cases with a þ -thalassaemia, 86.1% showed a positive result; 100 out of 103 Hb E carriers, all homozygous Hb E and b-thalassaemia trait were negative. Nine out of 17 cases with b-thalassaemia/Hb E disease, and one case of double heterozygote for Hb Q-Thailand and Hb E returned positive results. The overall sensitivity and specificity of the IC strip assay for detecting a 0 -thalassaemia were 100% and 73.1%, respectively. Conclusion: The results showed a high sensitivity for screening for a 0 -thalassaemia using IC strip assay for Hb Bart's. This simple method, used in combination with conventional screening protocols, should lead to a significant reduction in the number of referral cases for DNA analysis. Cost effectiveness in each population should be taken into consideration.

Evaluation of an immunochromatographic strip test for alpha‐thalassaemia screening

“…It removes the time-consuming microscopy examination in the HbH-i and gives an improved turnaround time. Both our study and the published studies 8,9,16 showed the ICT is more sensitive and more specific than the HbH-i.…”

Screening of (–SEA) α-thalassaemia using an immunochromatographic strip assay for the ζ-globin chain in a population with a high prevalence and heterogeneity of haemoglobinopathies

“…This might indicate cross-reactivity of the anti-ζ-globin chain with other globin chains. A similar finding with 50 out of 63 (79.4%) false positives from α + -thalassaemia has been observed for the IC strip assay for Hb Bart's 10. Further details on the titre of the monoclonal antibodies used in the kit and cross-reactivity with other globin chains are not available.…”

“…Although this indicates a sensitivity of 100% for the IC strip assay in screening for (– SEA ) α 0 -thalassaemia, a relatively low specificity was noted (85%). We have previously shown that an IC strip assay for Hb Bart's could yield a similar diagnostic performance with a sensitivity of 100% and a specificity of 73.1% 10. This is in contrast to the spectrophotometric or fluorescence microscope-based ζ-globin chain detection by ELISA reported previously with a sensitivity of 100% and specificity ranging between 94% and 98% 16 22 23.…”

“…The (– FIL ) α 0 - thalassaemia deletion has not been found in the region and the prevalence of (– THAI ) α 0 -thalassaemia is very low 25. It is conceivable that using this proposed protocol in combination with other additional tests—for example, the Hb H inclusion test 8 or IC strip assay for Hb Bart's9 10—would help in preventing a misdiagnosis of cases with these rare α 0 -thalassaemia defects.…”

“…This could lead to an unnecessary workload and expenses of post-screening Hb and DNA analyses. In order to minimise this, several approaches have been introduced into the screening protocol—for example, the use of a modified Hb H inclusion test in combination with OF and DCIP tests7 8 and identification of Hb Bart's 9 10. While the Hb H inclusion test is laborious and the result is highly observer-dependent, identification of Hb Bart's is affected by other forms of thalassaemia, especially α + -thalassaemia which is commonly encountered in the region.…”