Which of the following haemoglobin (Hb) estimation will be diagnostically helpful in a in a case of beta thalassemia triat

Beta thalassemia trait characterized by raised levels of HbA2 Normal hemoglobin is composed predominantly of HbA1 - which is composed of 2 alpha chains and 2 beta chains. In beta thalassemia trait, there is decrease in production of beta chains of hemoglobin. But since the defect is minor, they will not have any clinical features and the peripheral smear may be normal. But there will be a compensatory increase in HbA2 which is composed of 2 alpha chains and 2 delta chains. Normally HbA2 constitutes about 1.5 to 3.5% of total hemoglobin. But in beta thalassemia trait, this increases to about 3.6 to 8%. Reference: Ghai essential of pediatrics, eighth edition, p.no:341