Most α-thalassemia cases are caused by deletions of the structural α-globin genes. The degree of microcytosis and hypochromia has been correlated with the number of affected α-globin genes, suggesting a promising role of hematologic parameters as predictive diagnostic tools. However, cut-off points for these parameters to discriminate between the different subtypes of α-thalassemia are yet to be clearly defined. Six hematologic parameters (RBC, Hb, MCV, MCH, MCHC and RDW) were evaluated in 129 cases of deletional α-thalassemia (56 heterozygous α⁺ thalassemia, 36 homozygous α⁺ thalassemia, 29 heterozygous α⁰ thalassemia and 8 cases of Hb H disease). A good correlation between the number of deleted alpha genes and MCV (r = -0.672, p < 0.001), MCH (r = -0.788, p < 0.001) and RDW (r = 0.633, p < 0.001) was observed. The presence of an α⁰ allele should be discarded in individuals with microcytosis without iron deficiency and normal values of Hb A₂ and Hb F with MCH < 23.40 pg. Furthermore, MCH < 21.90 pg and/or MCV < 70.80 fL are strongly suggestive of the presence of one α⁰ allele. Finally, an accurate presumptive diagnosis of Hb H disease can be made if both RDW ≥ 20% and MCH < 19 pg are seen.
Keywords: alpha; cut-off; deletional; differential diagnosis; microcytic anemia; number of genes; thalassemia.