A Newly Modified Hemoglobin H Inclusion Test as a Secondary Screening for α0-Thalassemia in Southeast Asian Populations

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Abstract

Screening for α0-thalassemia is usually associated with a high false-positive rate, leading to an unnecessary PCR workload for accurate diagnosis. We have developed a modified Hb H inclusion test for use as a secondary screening. This test was performed on young red blood cell enriched fractions using dextran sedimentation. The study was performed in 100 subjects positive on initial screening. Confirmatory tests included Hb analysis and a multiplex PCR assay to identify α0-thalassemia deletions. A modified Hb H inclusion test was positive in 31 cases, 30 of whom were α0-thalassemia carriers (97%). The remaining case (3.0%) was homozygous for α+-thalassemia. The remaining 69 cases with a negative Hb H inclusion test included normal subjects, α+-thalassemia carriers and β-thalassemia carriers. Two of them (2/69, 3.0%) were found to be double heterozygotes for β0-thalassemia and α0-thalassemia. The overall sensitivity and specificity of the modified Hb H inclusion test for screening of α0-thalassemia were 94.0 and 99.0%, respectively. Therefore, we recommend the use of this test in combination with Hb analysis to exclude cases with αβ-thalassemia. This should lead to a significant reduction in the number of cases referred for PCR analysis of α0-thalassemia by about 50.0%.

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