Hemoglobin A2 (HbA2) is a normal variant of hemoglobin A that consists of two alpha and two delta chains (α2δ2) and is found at low levels in normal human blood. Hemoglobin A2 may be increased in beta thalassemia or in people who are heterozygous for the beta thalassemia gene.
HbA2 exists in small amounts in all adult humans (1.5–3.1% of all hemoglobin molecules) and is approximately normal in people with sickle-cell disease.[1] Its biological importance is not yet known.
HbA2 may seem physiologically minor, but it plays a very crucial role in identifying the beta-thalassemia traits, also known as BTT, and identifying other hemoglobin disorders.[2] Human hemoglobin is made up of two different chains, this includes alpha-globin and beta-globin. In the blood, there are two different variants, HbA and HbA2, and these variants only differ by 10 amino acids. These two variants have distinctions with the alpha and beta-globin chains. HbA2 is a vital component for screening programs targeting beta-thalassemia and hemoglobin pathogens. Typically the normal HbA2 levels range from 2.1% to 3.2%, but these values may change based on individual factors and different hemoglobin or hematological patterns.[3] Testing HbA2 levels can be challenging because different disorders can cause it to have higher or lower values. Testing for the beta-thalassemia trait is usually identified when the value of HbA2 is higher than 3.5%.[3] HbA2 is also important for diagnosing sickle cell disease, which is one of the most prevalent genetic conditions. Sickle cell disease exhibits characteristics of either homozygous hemoglobin S, also known as Hb S, or Hb S paired with another hemoglobin variant. In diagnosing patients with sickle cell, HbA2 is taken into account alongside a complete blood count, family history, and clinical data.[4]
^"Clinical Practice Guideline for Sickle Cell Disease/Trait". American Society of Aerospace Medicine Specialists. Retrieved 3 May 2013.
^Figueiredo MS (September–October 2015). "The importance of hemoglobin A2 determination". Revista Brasileira de Hematologia e Hemoterapia. 37 (5): 287–289. doi:10.1016/j.bjhh.2015.06.002. PMC 4685102. PMID 26408359.
^ abGiambona A, Passarello C, Renda D, Maggio A (December 2009). "The significance of the hemoglobin A(2) value in screening for hemoglobinopathies". Clinical Biochemistry. Hemoglobin Disorders. 42 (18): 1786–1796. doi:10.1016/j.clinbiochem.2009.06.026. PMID 19591816.
^da Fonseca SF, Amorim T, Purificação A, Gonçalves M, Boa-Sorte N (September–October 2015). "Hemoglobin A2 values in sickle cell disease patients quantified by high performance liquid chromatography and the influence of alpha thalassemia". Revista Brasileira de Hematologia e Hemoterapia. 37 (5): 296–301. doi:10.1016/j.bjhh.2015.05.005. PMC 4685046. PMID 26408362.
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