From the Guidelines
Alpha thalassemia is diagnosed through a combination of complete blood count (CBC), hemoglobin electrophoresis, and genetic testing, with definitive diagnosis requiring DNA analysis to identify specific deletions or mutations in the alpha-globin genes (HBA1 and HBA2) 1.
Diagnostic Criteria
The diagnostic criteria for alpha thalassemia include:
- Complete blood count (CBC) showing microcytic, hypochromic anemia with normal or elevated red blood cell count
- Hemoglobin electrophoresis to detect abnormal hemoglobin patterns
- Genetic testing to identify specific deletions or mutations in the alpha-globin genes (HBA1 and HBA2)
- Family studies for genetic counseling purposes
- Prenatal diagnosis through chorionic villus sampling or amniocentesis with DNA analysis for severe forms
Importance of Genetic Testing
Genetic testing is crucial in diagnosing alpha thalassemia as it has four clinical presentations depending on how many of the four alpha-globin genes are affected: silent carrier (one gene affected), alpha thalassemia minor (two genes affected), Hemoglobin H disease (three genes affected), and Hemoglobin Bart hydrops fetalis (all four genes affected) 1.
Clinical Considerations
A thorough clinical history, including ethnic background, is important as alpha thalassemia is more common in individuals of Mediterranean, African, Middle Eastern, and Southeast Asian descent. In cases of nonimmune hydrops fetalis, DNA testing for alpha-thalassemia is recommended if the mean corpuscular volume (MCV) of parents is less than 80 fL 1.
From the Research
Diagnostic Criteria for Alpha Thalassemia
The diagnostic criteria for alpha thalassemia involve a combination of screening tests and genetic tests.
- Screening tests include:
- Complete blood count
- Blood smear
- Hemoglobin quantification by high-performance liquid chromatography (HPLC) or capillary electrophoresis (CE)
- Genetic tests include:
- Molecular analysis for confirmatory diagnosis
- Techniques such as multiplex gap-polymerase chain reaction, single-tube multiplex polymerase chain reaction, multiplex ligation-dependent probe amplification, and loop-mediated isothermal amplification to detect common deletions of alpha-thalassemia
- Reverse dot blot analysis and single-tube multiplex polymerase chain reaction to detect non-deletion mutations of the alpha-globin gene
- Sanger sequencing to detect non-deletion mutations of alpha-thalassemia
- Next-generation sequencing (NGS) to detect both deletion and point mutations of alpha-thalassemia 2
Laboratory Diagnosis
Laboratory diagnosis of thalassemia requires a number of tests, including:
- Red blood cell indices
- Hemoglobin (Hb) analysis by HPLC or CE
- DNA analysis for specific thalassemia mutation diagnosis
- Various molecular techniques, such as PCR, gap-PCR, and DNA sequencing, to detect point mutations and large deletions 3, 4
Clinical Presentation
The clinical presentation of alpha-thalassemia varies depending on the genotype, ranging from a silent or mild carrier state to severe, transfusion-dependent or lethal disease 5
- Alpha-thalassemia major results in hydrops fetalis and is often fatal at birth 6
- Alpha-thalassemia intermedia has variable presentations based on gene mutation or deletion, with mild forms requiring only monitoring but more severe forms leading to symptomatic anemia and requiring transfusion 6
Diagnosis Techniques
Various techniques are used to diagnose alpha-thalassemia, including: