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Primary screening for thalassemia and hemoglobinopathies usually involves an accurate blood count using an expensive electronic blood cell counter. A cheaper alternative method was tested by using a modified osmotic fragility (OF) test and a modified dichlorophenolindophenol (DCIP) test. Altogether 423 pregnant Thai women participated in this project. Hemoglobin patterns and globin genotypes were determined using an automated high-performance liquid chromatography analyzer and polymerase chain reaction analysis of α- and β-globin genes. Among the 423 subjects, 264 (62.4%) carried thalassemia genes. The combined OF and DCIP tests detected all pregnant carriers of the 3 clinically important thalassemias, ie, α-thalassemia, β-thalassemia, and hemoglobin E with a sensitivity of 100.0%, specificity of 87.1%, positive predictive value of 84.5%, and negative predictive value of 100.0%, which show more effectiveness than these values for the standard method based on RBC counts. A combination of modified OF and DCIP tests should prove useful and applicable to prenatal screening programs for thalassemia and hemoglobinopathies in communities with limited facilities and economic resources.
Thalassemia and hemoglobinopathies, the most common inherited disorders of hemoglobin (Hb) synthesis, are among the major public health problems in many areas of the world, including Southeast Asia. Although gene-gene interactions in this population can lead to several thalassemia syndromes, 3 targeted for prevention and control measures are homozygous α-thalassemia causing the Hb Bart hydrops fetalis, homozygous β-thalassemia, and β-thalassemia/Hb E. Therefore, in a prevention and control program, rapid, accurate, and inexpensive screening protocols to identify carriers of α-thalassemia, β-thalassemia, and Hb E, especially in a prenatal population at risk for Hb disorders, are essential.
Conventionally, the primary screening method for all forms of thalassemia relies on hematologic index cutoffs, which involves an accurate blood count using an electronic cell counter. Individuals with mean corpuscular volume (MCV) values less than 80 µm (<80 fL) and mean corpuscular hemoglobin (MCH) values less than 27 pg should be examined further to confirm or exclude the diagnoses of α-thalassemia and β-thalassemia. This, however, requires an expensive electronic blood cell counting apparatus and cannot be applied in rural areas where laboratory facilities and economic resources are limited.
It has been demonstrated that a single-tube osmotic fragility (OF) test with 0.36% saline solution might be an attractive alternative to identify carriers of α- and β-thalassemias. Recently it was demonstrated that the use of 0.34% instead of 0.36% saline solutions could greatly improve the specificity of the OF test for α-thalassemia and β-thalassemia, but an Hb E carrier would be missed. A combined modified OF test and modified dichlorophenolindophenol (DCIP) test for Hb E has been proposed for screening in rural communities of Southeast Asia. However, this screening protocol might not be appropriate for pregnant women because anemia might be more prevalent and severe owing to physiologic changes and/or iron deficiency. Therefore in this study, the effectiveness of the combined modified OF test and modified DCIP test for the identification of α-thalassemia, β-thalassemia, and Hb E in pregnancy was tested and compared with other standard screening protocols involving measurement of RBC indices.
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