**Core Concept:** HbA2 is a normal constituent of human hemoglobin, consisting of alpha-globin chains. It is typically found in concentrations between 2.5% and 4.5% in adult humans. HbA2 is not directly related to any specific disease or condition, but its elevation can be indicative of a hemoglobinopathy.

**Why the Correct Answer is Right:** HbA2 is primarily elevated in cases of beta-thalassemia minor, also known as beta-thalassemia intermedia. Beta-thalassemia minor is a genetic disorder characterized by reduced synthesis of beta-globin chains. When beta-globin chain synthesis is reduced, alpha-globin chains are produced in excess, leading to increased HbA2 levels.

**Why Each Wrong Option is Incorrect:**

A. Haemolytic anaemia (increased destruction of red blood cells): HbA2 levels are typically normal or slightly elevated in cases of haemolytic anaemia, as it is not primarily caused by abnormal alpha-globin chains.

B. Sickle cell disease (mutated haemoglobin HbS): HbA2 levels are normal in sickle cell disease, as the primary abnormality is in the beta-globin chains, not alpha-globin chains.

C. Polycythaemia (increased red blood cell mass): HbA2 levels are not affected by changes in red blood cell mass, as the question pertains to abnormal alpha-globin chains and not the overall red blood cell mass.

D. Iron deficiency anaemia (reduced red blood cell mass): HbA2 levels are not affected by changes in red blood cell mass, as mentioned before.

**Clinical Pearl:** Elevated HbA2 levels should prompt an assessment for beta-thalassemia trait, which may assist in genetic counselling and prenatal diagnosis for affected offspring.

**Correct Answer:** D. Haemolytic anaemia (increased destruction of red blood cells)

In conclusion, elevated HbA2 levels are primarily found in individuals with beta-thalassemia minor, while other options involve abnormalities in beta-globin chains and do not lead to elevated HbA2 levels. Haemolytic anaemia results in increased destruction of red blood cells, which can lead to elevated HbA2 levels due to increased alpha-globin chain production.