What is the approach to diagnosing beta thalassemia?

Diagnostic Approach to Beta Thalassemia

Beta thalassemia diagnosis begins with complete blood count (CBC) showing microcytic hypochromic anemia with MCV typically 60-70 fL and MCH 19-23 pg, followed by hemoglobin electrophoresis or HPLC demonstrating elevated HbA2 levels (>3.5%), and confirmed by DNA analysis when needed for specific mutation identification or prenatal diagnosis. 1, 2, 3

Initial Laboratory Screening

Complete Blood Count Analysis

• MCV is markedly reduced (60-70 fL) and MCH is significantly decreased (19-23 pg) in beta-thalassemia carriers, distinguishing them from alpha-thalassemia carriers who show only slight to moderate reductions 3
• Red blood cell count is typically normal or elevated, which helps differentiate from iron deficiency anemia where RBC count is usually low 4, 1
• RDW ≤14.0% suggests thalassemia trait, while RDW >14.0% suggests iron deficiency anemia 4, 1

Critical Step: Iron Status Assessment

• Measure serum ferritin before proceeding with hemoglobin analysis because iron deficiency can falsely lower HbA2 levels and mask beta-thalassemia trait diagnosis 4, 1
• If iron deficiency is present (ferritin below reference range), provide iron replacement therapy before performing hemoglobin electrophoresis, as concurrent iron deficiency will invalidly suppress HbA2 elevation 4, 1

Peripheral Blood Smear

• Examine for microcytic, hypochromic red blood cells with target cells and basophilic stippling 1, 2
• Reticulocyte count helps distinguish between decreased production versus increased destruction patterns 1

Definitive Hemoglobin Analysis

HbA2 Measurement (After Iron Repletion)

• HbA2 determination is the most decisive test for beta-thalassemia carrier detection, with levels >3.5% diagnostic for beta-thalassemia trait 3
• Perform using either high-performance liquid chromatography (HPLC) or capillary zone electrophoresis (CE), both providing qualitative and quantitative analysis 2
• Interpretation under CE requires caution because HbA2 is clearly separated from HbE, and alpha-thalassemia gene interactions can affect HbA2/E levels 2

Additional Hemoglobin Fractions

• Measure HbF levels, which may be mildly elevated in some beta-thalassemia variants 2, 3
• Identify any abnormal hemoglobin variants that may coexist 2

Molecular DNA Analysis

When DNA Testing Is Required

• DNA analysis is essential to predict severe transfusion-dependent (beta-thalassemia major) and intermediate-to-mild non-transfusion-dependent cases 3
• Required for prenatal diagnosis using chorionic villus sampling (CVS) at 10-13 weeks or amniocentesis at 15-20 weeks when both parents are carriers 4, 3
• Necessary when hemoglobin analysis results are equivocal or when specific mutation identification is needed for genetic counseling 2, 3

Molecular Techniques Available

• Point mutation detection methods for beta-thalassemia mutations 2
• Next-generation sequencing (NGS) provides accurate diagnosis and can detect mutations that may be misdiagnosed by conventional techniques, though cost remains a limitation 2

Prenatal Screening Algorithm

Initial Maternal Assessment

• All pregnant women should undergo CBC screening with particular attention to MCV, as thalassemia carriers typically have MCV <80 fL 4
• If MCV <80 fL, proceed with hemoglobin analysis after excluding iron deficiency 4, 1

Partner Testing When Mother Is Carrier

• Partner screening is mandatory when the pregnant woman is identified as a thalassemia carrier to determine couple's risk 4
• Partner should have CBC with MCV measurement, and if MCV <80 fL, proceed with hemoglobin analysis 4

At-Risk Couple Management

• When both parents are carriers, they face a 25% risk with each pregnancy of having a child with beta-thalassemia major 4
• Offer prenatal diagnosis via CVS (10-13 weeks) or amniocentesis (15-20 weeks) for DNA-based mutation detection 4, 3
• Provide clear, nondirective genetic counseling covering carrier state characteristics, disease risks to the child, and all available options 4

Common Diagnostic Pitfalls to Avoid

Iron Deficiency Masking

• The most critical pitfall is performing HbA2 measurement before correcting iron deficiency, which will falsely lower HbA2 and cause missed diagnosis 4, 1
• Always measure ferritin and correct iron deficiency before final thalassemia assessment 4, 1

Misdiagnosis as Iron Deficiency Anemia

• Beta-thalassemia presenting with microcytic anemia in adulthood may be misdiagnosed as treatment-resistant iron deficiency anemia 5
• Key distinguishing features: normal or elevated RBC count, RDW ≤14.0%, and lack of response to iron supplementation 4, 1, 5

Other Conditions to Exclude

• Lead poisoning, anemia of chronic inflammation, and sickle cell trait can present with similar red cell indices 1
• Delta-thalassemia defects can disturb HbA2 determination in beta-thalassemia carrier detection 3

Ethnicity Considerations

• Failure to consider ethnicity can lead to missed diagnoses, as beta-thalassemia predominates in Mediterranean, Middle Eastern, and South Asian populations 4