What is the management approach for elevated Hemoglobin A2 (HbA2) levels?

Management of Elevated Hemoglobin A2 (HbA2) Levels

Elevated HbA2 levels (>3.5%) are most commonly diagnostic of beta-thalassemia trait and require genetic counseling, while normal or low HbA2 levels may mask underlying hemoglobinopathies that need molecular genetic testing for definitive diagnosis. 1, 2

Diagnostic Interpretation of HbA2 Levels

When HbA2 is Elevated (>3.5%)

• Beta-thalassemia trait is the primary diagnosis when HbA2 levels exceed 3.5% in the presence of microcytic hypochromic anemia (MCV <80 fL, MCH <27 pg). 1, 3

• Confirm with complete blood count showing reduced MCV and MCH, which are typical features of heterozygous beta-thalassemia. 3

• Genetic counseling is mandatory for all patients with confirmed beta-thalassemia trait to discuss inheritance patterns and prenatal diagnosis options for at-risk couples. 4, 2

• Rare cases exist where HbA2 elevation occurs without beta-globin gene defects—these represent isolated genetic traits transmitted dominantly with normal red cell indices and globin chain synthesis. 3

When HbA2 is Normal or Low (<2.5%)

• Do not exclude beta-thalassemia trait based solely on normal HbA2 levels, as several conditions mask the expected HbA2 elevation. 1, 2

• Alpha-thalassemia reduces HbA2 levels to 1.39-2.43%, and double heterozygotes for alpha and beta-thalassemia may present with normal MCV/MCH but still have beta-thalassemia. 1

• Delta-thalassemia (δ+ or δ0) presents with HbA2 levels of 1.70-1.77%. 1

• HbA2 structural variants (mutations in the delta-globin gene) reduce measured HbA2 to approximately 1.75-1.76% and can completely mask coexisting beta-thalassemia trait. 1, 2

• When clinical suspicion for beta-thalassemia exists despite normal HbA2 (microcytic anemia refractory to iron, family history), proceed directly to molecular genetic testing of alpha, beta, and delta-globin genes. 1, 2

Laboratory Workup Algorithm

Initial Testing

• Measure HbA2 and HbF levels using ion exchange high-performance liquid chromatography (HPLC). 1, 5

• Perform capillary zone electrophoresis to identify hemoglobin variants. 1

• Complete blood count with peripheral smear to evaluate red cell morphology and other cell lines. 6

When HPLC Shows Abnormal Peaks

• HbA2' variant elutes in the S window on HPLC with diagnostic criteria: HbA2 ≤2%, S window peak 1-2%, absence of HbS, HbG, and HbC. 5

• HbA2' is hematologically silent but may coexist with beta-thalassemia—suspect double heterozygosity when sum of HbA2 + HbA2' exceeds 4%. 5

• Reversed-phase HPLC can determine specific globin chain composition when structural variants are suspected. 1

Molecular Genetic Testing Indications

• Mandatory when: microcytic anemia persists with normal HbA2, family history suggests hemoglobinopathy, or genetic counseling/prenatal diagnosis is needed. 1, 2

• Sequence alpha, beta, and delta-globin genes using automatic sequencing. 1

• Perform multiplex PCR for alpha-globin gene deletions. 1

Clinical Management Considerations

For Confirmed Beta-Thalassemia Trait

• No transfusion therapy is required for asymptomatic carriers with stable hemoglobin levels. 4

• Avoid iron supplementation unless documented iron deficiency coexists (ferritin <30 ng/mL), as thalassemia trait causes microcytosis without iron deficiency. 4

• Screen at-risk couples (both partners carriers) for prenatal diagnosis options to prevent homozygous beta-thalassemia major. 4

For Compound Heterozygotes

• Double heterozygotes for alpha/beta-thalassemia or beta-thalassemia/HbA2 variants may have normal red cell indices but still require genetic counseling. 1, 2

• Family studies are essential to determine inheritance patterns and identify at-risk relatives. 2

Common Diagnostic Pitfalls

• Never diagnose iron deficiency anemia based solely on microcytosis—always measure HbA2 to exclude thalassemia trait, as iron therapy will not correct thalassemic microcytosis. 1, 3

• HbS, glycosylated HbC, and HbG2 interfere with HbA2' detection on HPLC and may lead to misdiagnosis. 5

• Normal HbA2 does not exclude beta-thalassemia when delta-globin mutations or alpha-thalassemia coexist—maintain high clinical suspicion with persistent microcytic anemia. 1, 2

• Rigorous interpretation of phenotypic data is crucial to avoid overlooking beta-thalassemia trait masked by HbA2 variants, as this diagnosis is essential for genetic counseling. 2