Diagnosis of Alpha Thalassemia
Begin with a complete blood count showing microcytosis (MCV 60–70 fL) and normal or near-normal RDW (≤14%), then confirm normal iron stores with ferritin >30 µg/L and transferrin saturation >20%, and proceed directly to molecular genetic testing because hemoglobin electrophoresis cannot reliably detect alpha thalassemia. 1, 2, 3
Initial Screening: Red Blood Cell Indices
Microcytosis with preserved RDW is the hallmark finding—alpha thalassemia carriers typically show MCV 60–70 fL with RDW ≤14%, distinguishing it from iron deficiency which usually presents with RDW >14%. 1, 4, 3
Mean corpuscular hemoglobin (MCH) is markedly reduced to 19–23 pg in alpha thalassemia carriers, though the reduction may be slight to moderate depending on the number of deleted alpha genes. 3
Red blood cell count is typically elevated or high-normal despite the microcytosis, which helps differentiate thalassemia from iron deficiency where RBC count is usually low. 3
Exclude Iron Deficiency Before Proceeding
Measure serum ferritin and transferrin saturation to rule out iron deficiency—ferritin >30 µg/L combined with transferrin saturation >20% effectively excludes iron deficiency and allows progression to thalassemia-specific testing. 1, 4
Do not proceed to hemoglobin electrophoresis or molecular testing until iron deficiency is excluded, as iron studies must be normal and microcytosis must persist before ordering costly genetic tests. 1, 4
Iron deficiency is the most common cause of microcytosis worldwide and must be systematically ruled out even in high-risk ethnic populations (Mediterranean, African, Southeast Asian). 1, 4
Hemoglobin Analysis: Limited Utility in Alpha Thalassemia
Hemoglobin electrophoresis by HPLC or capillary electrophoresis has limited diagnostic value for alpha thalassemia because most alpha thalassemia carriers show normal or only slightly reduced HbA₂ levels, unlike beta thalassemia where HbA₂ is elevated. 2, 3
In alpha thalassemia carriers, HbA₂ can be lower than normal (often <3.5%), which assumes diagnostic significance only when iron deficiency has been excluded. 3
Hemoglobin electrophoresis is useful primarily to exclude beta thalassemia or hemoglobinopathies (such as HbE) that may coexist with alpha thalassemia. 2, 5
Definitive Diagnosis: Molecular Genetic Testing
Molecular DNA analysis is essential and required to confirm alpha thalassemia carrier status because hematological parameters and hemoglobin studies cannot provide a definitive diagnosis. 6, 3
Multiplex gap-PCR is the most widely used method to detect common alpha thalassemia deletions (--SEA, --Thai, -α3.7, -α4.2) and should be the first-line molecular test. 6, 2, 7
Multiplex ligation-dependent probe amplification (MLPA) can detect both common and rare deletions and is particularly useful when gap-PCR is negative but clinical suspicion remains high. 6
Sanger sequencing or targeted next-generation sequencing (NGS) is necessary to detect non-deletion (point) mutations in the HBA1 and HBA2 genes, which account for approximately 20–30% of alpha thalassemia cases. 6, 2, 8, 7
Next-generation sequencing panels targeting HBA1, HBA2, and HBB genes are increasingly recommended because they detect both deletions and point mutations in a single assay, identifying rare variants that conventional methods miss. 2, 5, 8, 7
Genetic Counseling and Family Screening
All confirmed alpha thalassemia carriers must receive genetic counseling about the autosomal recessive inheritance pattern—if both partners are carriers, each pregnancy carries a 25% risk of Hb Bart's hydrops fetalis (lethal), 50% risk of carrier status, and 25% chance of being unaffected. 1
Partner screening is mandatory for reproductive-age couples or those from high-risk ethnic groups (Southeast Asian, Mediterranean, African) to assess the risk of having a child with severe alpha thalassemia. 1, 9
Siblings and children of a carrier have a 50% probability of being carriers and should be offered screening with CBC and molecular testing. 1
Prenatal diagnosis using chorionic villus sampling and molecular analysis is available for at-risk couples and should be discussed during genetic counseling. 3, 10
Critical Pitfalls to Avoid
Do not assume all microcytosis in high-risk ethnicities is thalassemia—iron deficiency remains the most common cause worldwide and must be excluded with ferritin and transferrin saturation before attributing findings to thalassemia. 1, 4
Do not rely on hemoglobin electrophoresis alone to diagnose alpha thalassemia—unlike beta thalassemia where HbA₂ is elevated, alpha thalassemia carriers typically have normal or low HbA₂, making electrophoresis unreliable for diagnosis. 2, 3
Do not use hemoglobin electrophoresis as a first-line test—iron studies must be normal and microcytosis must persist before electrophoresis is ordered, as the test is costly and unnecessary when iron deficiency is present. 1
Do not overlook combined deficiencies—alpha thalassemia can coexist with iron, vitamin B12, or folate deficiency; an elevated RDW despite underlying thalassemia suggests such combined deficiencies and requires additional workup. 1, 4
Do not give iron supplementation unless true iron deficiency is documented (ferritin <30 µg/L or transferrin saturation <20%)—unnecessary iron in thalassemia carriers provides no benefit and may cause gastrointestinal side effects or iron overload. 1, 4
Do not stop at conventional gap-PCR if clinical suspicion is high—approximately 17% of rare alpha thalassemia variants are missed by routine molecular methods and require NGS for detection. 8, 7