Testing for Thalassemia
Initial laboratory testing for thalassemia should include complete blood count (CBC) with red blood cell indices, hemoglobin electrophoresis or high performance liquid chromatography (HPLC), and molecular genetic testing when appropriate. 1, 2
Initial Screening Tests
- 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, contrasting with iron deficiency anemia 1
- 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
- Peripheral blood smear examination is essential to confirm the size, shape, and color of red blood cells 1
- Serum ferritin should be measured to rule out concurrent iron deficiency, which can mask thalassemia trait characteristics 1
Hemoglobin Analysis
- Hemoglobin electrophoresis or HPLC should be performed to detect abnormal hemoglobin patterns 2, 3
- HbA2 measurement is crucial for diagnosing beta-thalassemia trait (typically elevated) 1, 3
- Important: HbA2 measurement should be performed after iron deficiency has been corrected, as iron deficiency can falsely lower HbA2 levels 1
- Quantitation of HbF is also recommended as part of the screening process 3
- For suspected alpha-thalassemia with normal hemoglobin electrophoresis but microcytosis/hypochromia, brilliant cresyl blue staining should be performed to identify H bodies 3
Molecular Genetic Testing
- DNA analysis is required for definitive diagnosis, especially for alpha-thalassemia which may not show abnormal hemoglobin patterns on electrophoresis 2, 4
- Molecular testing can identify specific mutations in the alpha or beta globin genes 2
- Massively parallel sequencing (next-generation sequencing) enables more precise molecular diagnosis of thalassemia/hemoglobinopathy 2
- For alpha-thalassemia, testing for common deletions in the alpha-globin gene is typically performed 3
- For beta-thalassemia, point mutation analysis of the beta-globin gene is conducted 4
Special Considerations
- If both partners are found to be carriers of thalassemia or hemoglobin variants, they should be referred for genetic counseling 3
- Prenatal diagnosis can be performed using cells obtained by chorionic villus sampling or amniocentesis 3
- For couples at risk of having a child with hemoglobin Bart's hydrops fetalis (four-gene deletion alpha-thalassemia), serial detailed fetal ultrasound for assessment of the fetal cardiothoracic ratio should be considered 3
- In pregnant women with hydrops fetalis on ultrasound who have an ethnic background with increased risk of alpha-thalassemia, immediate investigation of both parents' carrier status is recommended 3
Common Pitfalls to Avoid
- Concurrent iron deficiency can mask the typical laboratory findings of thalassemia trait, particularly HbA2 elevation in beta-thalassemia trait 1
- Lead poisoning, anemia of chronic inflammation, and sickle cell trait can present with similar red cell indices and must be excluded 1
- Testing for thalassemia should be considered in individuals with unexplained microcytic anemia that does not respond to iron therapy 4
- Failure to screen partners of identified carriers may miss couples at risk of having children with severe forms of thalassemia 3
By following this comprehensive testing approach, clinicians can accurately diagnose thalassemia and provide appropriate management and genetic counseling to affected individuals and carriers.