What is the initial workup for suspected thalassemia in a case of microcytic anemia?

Workup for Suspected Thalassemia in Microcytic Anemia

When thalassemia is suspected in a patient with microcytic anemia, first exclude iron deficiency with serum ferritin and transferrin saturation, then proceed directly to hemoglobin electrophoresis for beta-thalassemia detection and genetic testing for alpha-thalassemia confirmation. 1

Initial Laboratory Assessment

First-Line Iron Studies

• Measure serum ferritin as the most specific test to exclude iron deficiency, with levels <30 μg/L indicating low iron stores 2, 3
• Check transferrin saturation (TSAT), as thalassemia typically presents with normal or elevated ferritin and normal TSAT, distinguishing it from iron deficiency anemia 1
• In thalassemia, expect normal or elevated ferritin levels despite microcytic anemia, which is the key differentiating feature from iron deficiency 4

Red Blood Cell Indices Analysis

• Calculate the Mentzer index (MCV/RBC count): a value <13 suggests thalassemia trait while >13 suggests iron deficiency, with 98.7% sensitivity and 82.3% specificity for beta-thalassemia trait 5
• Evaluate RBC count: thalassemia typically shows elevated RBC count (>5 million/μL) despite low hemoglobin, whereas iron deficiency shows low RBC count 6, 5
• Assess RDW (red cell distribution width): RDW ≤14.0% with low MCV suggests thalassemia minor, while RDW >14.0% suggests iron deficiency 3

Definitive Diagnostic Testing

For Beta-Thalassemia

• Perform hemoglobin electrophoresis to detect elevated HbA2 (>3.5%) and/or elevated HbF, which confirms beta-thalassemia trait 4, 7
• This test reveals the characteristic hemoglobin pattern and is diagnostic for beta-thalassemia variants 1

For Alpha-Thalassemia

• Order genetic testing for alpha-globin gene deletions, as hemoglobin electrophoresis is typically normal in alpha-thalassemia trait and cannot confirm the diagnosis 4
• Alpha-thalassemia requires molecular genetic analysis since it lacks the characteristic HbA2 elevation seen in beta-thalassemia 8

Critical Diagnostic Pitfalls to Avoid

Concurrent Iron Deficiency

• Do not assume thalassemia is excluded if ferritin is low—approximately 6-9% of patients have co-existing iron deficiency and thalassemia trait 8
• In mixed cases, treat iron deficiency first with oral iron for 16 weeks, then repeat HbA2 screening after iron repletion, as iron deficiency can mask elevated HbA2 levels 5

Inflammation Considerations

• In the presence of inflammation, ferritin up to 100 μg/L may still indicate iron deficiency since ferritin is an acute phase reactant 2
• Consider C-reactive protein measurement to interpret ferritin levels in the context of inflammation 8

Algorithmic Approach

Step 1: Obtain CBC with indices (MCV, MCH, RBC count, RDW) 6, 7

Step 2: Check serum ferritin and transferrin saturation 1

Step 3: If ferritin is normal/elevated (>30 μg/L):

• Calculate Mentzer index
• Proceed to hemoglobin electrophoresis for beta-thalassemia 4, 5
• Order alpha-globin genetic testing if hemoglobin electrophoresis is normal but clinical suspicion remains high 4

Step 4: If ferritin is low (<30 μg/L):

• Treat with oral iron supplementation for 16 weeks 5
• Repeat ferritin and hemoglobin electrophoresis after iron repletion to unmask potential thalassemia trait 5

Additional Considerations

• Peripheral blood smear examination may show target cells, basophilic stippling, and nucleated RBCs in thalassemia, supporting the diagnosis 7
• Family screening and genetic counseling should be offered once thalassemia is confirmed, as this is an autosomal recessive condition with implications for family planning 1, 4
• In populations with high thalassemia prevalence, parallel screening for both iron deficiency and thalassemia in all children with microcytic anemia provides opportunities for carrier identification and prevention 8