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Introduction ⬇

Hemoglobin A2 (HbA2)

HbA2 levels have special application to the diagnosis of beta-thalassemia trait, which may be present even though the peripheral blood smear is normal. The microcytosis and other morphologic changes of beta-thalassemia trait must be differentiated from iron deficiency. Low MCV may be present in most patients with beta-thalassemia trait, but it does not differentiate iron-deficient patients.

This measurement is used in the investigation of hemolytic anemias for hemoglobinopathies, especially thalassemia and beta-thalassemia.

Normal Findings ⬆ ⬇

Adult: 1.5%–3.5% or 0.015–0.035 mass fraction

Newborns: 0%–1.8% or 0–0.018 mass fraction

Procedure ⬆ ⬇

  1. Draw a 5-mL venous sample of blood using a lavender-topped (EDTA) tube. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered.

  2. Perform electrophoresis.

Clinical Implications ⬆ ⬇

  1. Increased HbA2 occurs in:

    1. Beta-thalassemia major (3%–11%)

    2. Thalassemia minor (3.5%–7.5%)

    3. Thalassemia intermedia (6%–8%)

    4. Hb A/S (sickle cell trait) (15%–45%)

    5. Hb S/S (sickle cell disease) (2%–6%)

    6. S-beta-thalassemia (3.0%–8.5%)

    7. Megaloblastic anemia

    8. Hyperthyroidism

    9. VB12 or folate deficiency

  2. Decreased HbA2 occurs in:

    1. Untreated iron-deficiency anemia

    2. Sideroblastic anemia

    3. Hb H disease

    4. Erythroleukemia

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purpose and procedure. Assess for signs/symptoms of anemia, abdominal enlargement, frequent infections, epistaxis, anorexia, small body, large head, and possible intellectual disability.

  2. Provide genetic counseling.

  3. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing and treatment.

  2. Possible treatments include administering antibiotic drugs as ordered, providing folic acid supplements, and administering blood transfusions as ordered.

  3. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

  1. Blood transfusions before electrophoresis will interfere with results.

  2. High levels of Hb F usually are accompanied by low levels of A2.

  3. Hb C, Hb O, and Hb E interfere with the electrophoric migration of A2.

  4. If a patient with beta-thalassemia also has iron-deficiency anemia, the A2 may be normal; therefore, retesting may be needed after iron therapy.