What is the initial step in testing for thalassemia?

Initial Testing for Thalassemia

The initial step in testing for thalassemia should be a complete blood count (CBC) with red blood cell indices, particularly focusing on Mean Corpuscular Volume (MCV), Red Blood Cell (RBC) count, and Red Blood Cell Distribution Width (RDW). 1

Initial Laboratory Assessment

• Mean Corpuscular Volume (MCV) is typically low in thalassemia trait, with values often below the 5th percentile for age 1
• Red Blood Cell (RBC) count is often normal or elevated in thalassemia trait, in contrast to iron deficiency anemia where it is typically low 1, 2
• Red Blood Cell Distribution Width (RDW) is a critical differentiating factor: RDW ≤14.0% suggests thalassemia trait, while RDW >14.0% suggests iron deficiency anemia 1, 2
• Automated hematology analyzers can detect microcytosis and decreased hemoglobin content, which are hallmarks of thalassemic red blood cells 3

Second-Line Testing

After abnormal CBC results suggesting thalassemia:

• Serum ferritin measurement is essential to rule out concurrent iron deficiency, which can mask thalassemia trait characteristics 1
• Hemoglobin analysis should be performed using either:
  • High-performance liquid chromatography (HPLC) or
  • Capillary zone electrophoresis (CE)
  • Both systems provide qualitative and quantitative analysis of hemoglobin components 3
• HbA2 measurement is crucial but should be performed after iron deficiency has been corrected, as iron deficiency can falsely lower HbA2 levels 1

Definitive Diagnosis

• DNA analysis is required for specific thalassemia mutation diagnosis 4, 3
• Various molecular techniques are used for:
  • Point mutation detection in β-thalassemia
  • Large-deletion detection in α-thalassemia 3
• Next-generation sequencing (NGS) provides accurate diagnosis of thalassemia that may be misdiagnosed by conventional techniques, though cost remains a limitation 3

Common Pitfalls and Caveats

• Concurrent iron deficiency can mask the typical laboratory findings of thalassemia trait, particularly HbA2 elevation in beta-thalassemia trait 1
• Alpha-thalassemia 2 trait or HbCS trait may have red cell parameters similar to normal subjects, making them difficult to distinguish without genetic testing 2
• Lead poisoning, anemia of chronic inflammation, and sickle cell trait can present with similar red cell indices and must be excluded 1
• Coinheritance of alpha-thalassemia with beta-thalassemia or HbE trait can show variable red cell parameters, complicating diagnosis 2

Clinical Classification

• Modern classification divides thalassemia into:
  • Transfusion-dependent thalassemia
  • Non-transfusion-dependent thalassemia 5
• This classification encompasses all forms including α-thalassemia, hemoglobin E/β-thalassemia and combined α- and β-thalassemias 5

Following this diagnostic algorithm ensures proper identification of thalassemia variants, allowing for appropriate management and genetic counseling.