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HbA2

Hemoglobin electrophoresis Biomarker

Sample Needed

Collection Type: Blood

Body System

Related System: Hemoglobin electrophoresis

Overview

Hemoglobin A2 (HbA2) is a minor adult hemoglobin composed of two alpha and two delta globin chains (α2δ2). The HbA2 test measures the percentage of total hemoglobin made up by HbA2, typically by hemoglobin electrophoresis or high-performance liquid chromatography. Measurement is used to detect and help differentiate hemoglobin disorders most importantly to screen for beta‑thalassemia trait, which causes an elevated HbA2. Symptoms that prompt testing include lifelong mild microcytic anemia, unexplained microcytosis with normal iron studies, family history of thalassemia or hemoglobinopathy, and recurrent anemia not explained by iron deficiency. Age matters: newborns and very young infants have very low HbA2 until adult proportions are reached by about 4–6 months; gender has minimal effect.

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Test Preparation

Clinical history is required

Why Do I Need This Test

Profile: Hemoglobin electrophoresis / hemoglobinopathy panel - Symptoms: persistent microcytic anemia, pallor, fatigue, or family history of thalassemia/hemoglobinopathy - Diagnoses/monitoring: screening for beta‑thalassemia trait and some delta‑chain abnormalities - Reasons for abnormal levels: beta‑thalassemia increases HbA2; iron deficiency or recent transfusion can lower or mask elevations - Biological meaning: elevated HbA2 indicates reduced beta chain synthesis with compensatory delta synthesis; low HbA2 may reflect iron deficiency or delta‑chain defects - Family history of microcytic anemia or known thalassemia warrants testing

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Understanding Test Results

<2.0%: Low HbA2 may reflect iron deficiency anemia, recent red cell transfusion (dilution by donor cells), certain delta‑globin gene variants, or laboratory issues.
Low values can mask underlying beta‑thalassemia trait; iron studies and repeat testing after iron repletion are recommended.
2.0–3.3%: Normal adult range unlikely to be beta‑thalassemia trait by HbA2 alone.
Correlate with red cell indices and iron status.
3.5% and above: Elevated HbA2 strongly suggestive of beta‑thalassemia trait/carrier status.
Typical carrier values commonly fall in the ~3.5–6% (sometimes up to ~7%) range.
Values in the borderline zone (≈3.3–3.5%) require repeat testing, iron studies, and family studies.
Very high or discordant results (>7–10% or inconsistent with clinical picture): may indicate compound/inherited delta variants, mixed hemoglobinopathies, or analytical interference; further genetic testing and specialist review recommended.
Consider confounders (age <6 months, pregnancy, iron deficiency, recent transfusion) before final interpretation.

Normal Range

2.0-3.3 %

FAQs

Q: What does HbA2 indicate?

A: HbA2 is a minor adult hemoglobin made of two alpha and two delta chains. Its percentage reflects hemoglobin composition; normal values are about 2–3.5%. An elevated HbA2 (typically >3.5%) strongly suggests beta‑thalassemia trait and helps explain unexplained microcytic anemia. It’s interpreted with HbF levels and a full blood count to diagnose thalassemia and other hemoglobinopathies.

Q: What is the difference between HbA2 and HbA?

A: HbA (adult haemoglobin) is the major form in adults—α2β2—constituting about 95–98% of haemoglobin. HbA2 is a minor adult form—α2δ2—normally about 2–3.5%. Clinically, raised HbA2 (>3.5%) suggests β‑thalassaemia trait, while levels may be altered by other haemoglobinopathies or iron deficiency. HbA carries most oxygen; HbA2 has no major distinct function; measurement uses HPLC/electrophoresis.

Q: Is HbA2 normal in alpha thalassemia?

A: In alpha‑thalassemia, HbA2 is usually within the normal range because delta‑globin synthesis is not affected. Exceptions occur with coexisting conditions iron deficiency can lower HbA2, and co‑inheritance with beta‑thalassemia or some non‑deletional alpha variants may alter levels. Normal HbA2 therefore does not exclude alpha‑thalassemia; diagnosis often requires red‑cell indices, electrophoresis and genetic testing.

Q: What is HbF and HbA2?

A: HbF (fetal hemoglobin) contains two alpha and two gamma chains; it predominates in the fetus and has higher oxygen affinity. In adults it is normally <1% but rises in hereditary persistence of fetal hemoglobin and some hemoglobinopathies. HbA2 contains two alpha and two delta chains; it normally comprises about 2–3.5% of adult hemoglobin and is typically increased in beta‑thalassemia trait.

Q: Can I marry a thalassemia minor?

A: Yes. Thalassemia minor (trait) usually causes no serious health problems and does not prevent marriage or pregnancy. Important steps: have your partner tested (CBC and hemoglobin electrophoresis) and seek genetic counseling. If both are carriers, each pregnancy has a 25% chance of thalassemia major; options include prenatal diagnosis (CVS/amniocentesis), IVF with preimplantation testing, or informed reproductive planning.

Q: Can beta thalassemia be cured?

A: Beta thalassemia can be cured in some patients. Allogeneic hematopoietic stem cell (bone marrow) transplantation from a matched donor offers a potential cure, especially when performed early. Gene therapies are emerging as curative options for selected patients. Most people, however, receive lifelong supportive care—regular blood transfusions and iron chelation—which controls symptoms but is not curative. Eligibility and outcomes depend on age, disease severity and donor availability.