Testing Methods for Thalassemia
The most effective approach to testing for thalassemia involves a combination of complete blood count (CBC), hemoglobin analysis, and molecular genetic testing to identify mutations in globin genes. 1, 2
Initial Screening Tests
- Complete blood count (CBC) is the first step in thalassemia screening, with attention to red cell indices including microcytosis (MCV < 80 fL) and/or hypochromia (MCH < 27 pg) 3
- Hemoglobin electrophoresis or high-performance liquid chromatography (HPLC) should be performed to identify abnormal hemoglobin patterns 3, 4
- Quantitation of HbA2 and HbF levels is essential, as elevated HbA2 is a key marker for β-thalassemia carriers 3, 4
- Serum ferritin should be measured simultaneously to exclude iron deficiency anemia, which can also present with microcytosis 3
Additional Testing for Suspected Thalassemia
- If microcytosis and/or hypochromia are present with normal hemoglobin electrophoresis, brilliant cresyl blue staining should be performed to identify H bodies (indicative of α-thalassemia) 3
- In resource-limited settings, modified osmotic fragility (OF) test combined with dichlorophenolindophenol (DCIP) test can be used as an alternative screening approach with high sensitivity and specificity 5
Confirmatory Testing
- Molecular genetic testing is required to confirm α-thalassemia carrier status, as hemoglobin analysis alone may not be definitive 4
- DNA analysis using polymerase chain reaction (PCR) can identify specific deletions or mutations in α-globin and β-globin genes 1, 4
- For β-thalassemia, molecular analysis is not always required to confirm carrier status if HbA2 is elevated, but is necessary for identifying specific mutations 4
Testing in Pregnancy and Family Planning
- Carrier screening should be offered to individuals from high-risk ethnic populations, ideally before conception or early in pregnancy 3
- If both partners are found to be carriers, they should be referred for genetic counseling 3
- Prenatal diagnosis can be performed using DNA analysis of cells obtained through chorionic villus sampling or amniocentesis 3
Advanced Diagnostic Technologies
- Massively parallel sequencing (next-generation sequencing) enables more precise molecular diagnosis of thalassemia and hemoglobinopathies 1
- Mass spectrometry can be used as an alternative method for hemoglobin variant detection 1
Clinical Considerations
- Red cell indices alone cannot reliably distinguish between thalassemia and iron deficiency anemia, so additional testing is necessary 4
- The clinical classification of thalassemia into transfusion-dependent thalassemia (TDT) and non-transfusion-dependent thalassemia (NTDT) helps guide management decisions 2
Common Pitfalls to Avoid
- Failing to exclude iron deficiency, which can mask thalassemia traits by lowering HbA2 levels 4
- Relying solely on red cell indices without hemoglobin analysis can lead to misdiagnosis 4
- Not considering co-inheritance of δ-thalassemia, which can affect HbA2 levels and complicate diagnosis of β-thalassemia 4
- Overlooking the need for molecular testing in α-thalassemia, where hemoglobin analysis may appear normal 4