Гемоглобин A2 және бета-талассемияны анықтау

Variant of hemoglobin A
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. 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. 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. 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%.

Elevated HbA2 levels that surpass 3.5%, indicate a potential mutation in the beta globin genes. This potential mutation typically occurs in the 87 and 88 promoter region, which affects the proximal CACCC box. Another factor leading to increased HbA2 levels involves the deletion of bases that are placed adjacent to the beta globin genes. This deletion results in a heightened HbA2 levels due to removing the locus control regions in the beta promoter. This specific promoter is crucial for gene interactions with both gamma and beta globin genes, which also enables both genes to be expressed. This disorder is the most common autosomal recessive disorder in some countries. Hemoglobin A2 is employed to diagnose thalassemia disorders, encompassing both beta and alpha types. In beta thalassemia, affected individuals express elevated HbA2 levels, which can be a potential indicator of the heterozygous gene marker for the disorder. Normal levels range from 2.1 3.2%, but in the beta thalassemia disorder, the levels increase to 3.5 6.0%. Additionally, individuals with beta thalassemia exhibit a high red cell count and low hemoglobin levels. Individuals that express lower levels of hemoglobin A2, have the a0 thalassemia trait or homozygous gene for a+ thalassemia.

Hemoglobin A2 is a crucial role for screening and measuring for the beta thalassemia trait. Various laboratory methods exist, each providing different outcomes of accuracy. The different quantification methods of HbA2 relies on how effective it can be separated from other hemoglobin variants. Various laboratory methods are employed, such as cation exchange high performance liquid chromatography (HPLC), microcolumn chromatography, and cellulose acetate electrophoresis with elution. At first, cellulose acetate electrophoresis was utilized to measure HbA2, but this process proved to be too time consuming and labor intensive, making it impractical for large examinations or samples. Similar efficiency issues were encountered with other methods like IEF and scanning densitometry. These two methods separate proteins based on their isoelectric point. Chromatography, another commonly used method, demonstrated reliability in diagnosing individuals with the beta carrier gene. However, this method was also time consuming and inefficient when dealing with large sample numbers. Out of the various methods, the one that accurately measures HbA2 is HPLC. It is a reliable technique because it's able to accurately determine HbA2, HbF, and Hb variants. The various different Hb variants include: HbS, HbE, Hb Lepore, HbC, HbD and HbO Arab. There are several different factors that can contribute to the quantification of HbA2 to be inaccurately measured. These factors include column defects, batch variations, sample concentrations, dilution, calibration discrepancies, and the overall conditions of the samples.