Improvement of α° – Thalassemia Screening Using Combined Osmotic Fragility, Dichlorophenolindophenol and Hb H Inclusion Tests
Chaibunruang, A.; Pornphannukool, S.; Sae, N.-ung; Fucharoen, G.; Sanchaisuriya, K.; Fucharoen, S.
Clinical Laboratory 56(3-4): 111-117
2010
ISSN/ISBN: 1433-6510 PMID: 20476642 Document Number: 13041
Background: Screening for α°-thalassemia is usually done using osmotic fragility (OF) test or reduced erythrocyte indexes, both with high sensitivity, but accurate diagnosis requires PCR analysis. However, a low specificity of screening leads to unnecessary PCR workload during a massive population survey. We have established a more effective screening strategy using a combination of three simple tests. Methods: The study was done on 206 subjects with hypochromic microcytosis. Methods include osmotic fragility (OF) test, a dichlorophenolindophenol (DCIP) test for Hb E, a modified Hb H inclusion test, Hb and PCR analyses. Results: Initial screening with combined OF and DCIP tests identified 9 subjects with negative OF and DCIP tests (-/-), 58 with positive OF test but negative DCIP test (+/-), 13 with negative OF but positive DCIP tests (-/+) and 126 subjects with positive in both tests (+/+). Hb H inclusion was observed in 52 of 206 subjects including 1 in OF/DCIP (-/-), 31 in OF/DCIP (+/-) and 20 in OF/DCIP (+/+) groups. Among these 52 subjects, PCR analysis identified α°-thalassemia in 28 of 31 (+/-) and 16 of 20 (+/+) groups. Five of 106 subjects with negative Hb H inclusion in the (+/+) group were found to be heterozygous (3 of 5) and homozygous (2 of 5) Hb E co-inherited with α°-thalassemia. Conclusions: Hb H inclusion is not an appropriate screening test for α°-thalassemia in a region where Hb E is common. However performance of the test in the OF/DCIP (+/-) group would enhance the specificity of screening and result in elimination of almost 50 % of cases that would have required further PCR confirmation.
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