What laboratory tests and results are expected in a patient with thalassemia minor?

Laboratory Findings in Thalassemia Minor

Thalassemia minor presents with characteristic microcytic hypochromic anemia with low MCV (typically <80 fL, often 60-70 fL), normal or elevated RBC count, and crucially, a normal or low RDW (≤14.0%), which distinguishes it from iron deficiency anemia. 1, 2, 3

Complete Blood Count (CBC) Findings

Red Blood Cell Indices

• Mean Corpuscular Volume (MCV): Markedly reduced, typically below the 5th percentile for age, frequently <70-80 fL 1, 2, 3, 4
• Mean Corpuscular Hemoglobin (MCH): Significantly decreased, typically 19-23 pg 4
• Red Blood Cell (RBC) count: Normal or elevated, which is a key differentiating feature from iron deficiency where RBC count is typically low 1, 2, 3
• Red Blood Cell Distribution Width (RDW): Normal or minimally elevated (≤14.0%), which is the most critical discriminating parameter from iron deficiency anemia where RDW is >14.0% 1, 2, 3, 5

Hemoglobin Parameters

• Hemoglobin: Mild anemia or normal levels 4
• Peripheral blood smear: Microcytic hypochromic red cells with target cells 6, 4

Iron Studies

Normal iron parameters are expected and must be documented to confirm the diagnosis:

• Serum ferritin: Normal levels, which helps differentiate from iron deficiency anemia 1, 2, 3
• Iron/TIBC/saturation index: Normal 4

Hemoglobin Analysis

Beta-Thalassemia Minor

• HbA2: Elevated (typically >3.5%, often 4-6%) on hemoglobin electrophoresis or HPLC 2, 6
• HbF: May be mildly elevated (1-3%) 6
• Critical caveat: HbA2 measurement must be performed after iron deficiency has been corrected, as concurrent iron deficiency can falsely lower HbA2 levels and mask the diagnosis 1, 2

Alpha-Thalassemia Minor

• HbA2: Normal or slightly decreased 4
• Hemoglobin electrophoresis: Usually normal in alpha-thalassemia trait 3
• Molecular testing: Required to confirm alpha-thalassemia carrier status, as hemoglobin analysis alone is insufficient 4

Additional Laboratory Tests

• Reticulocyte count: Helps distinguish between decreased production versus increased destruction/loss of red blood cells 1, 2
• Peripheral blood smear examination: Essential to confirm microcytic hypochromic morphology and presence of target cells 1, 2

Critical Diagnostic Pitfalls

The following conditions must be excluded as they can mimic or mask thalassemia minor:

• Concurrent iron deficiency: The most common pitfall—iron deficiency can mask typical thalassemia findings, particularly HbA2 elevation in beta-thalassemia trait 1, 2
• Lead poisoning: Can present with similar red cell indices 1, 2
• Anemia of chronic inflammation: May show similar microcytosis 1, 2
• Sickle cell trait: Must be differentiated 1, 2

Diagnostic Algorithm

1. Initial screening: CBC with red cell indices showing MCV <80 fL 2
2. Differentiate from iron deficiency: Check RDW (≤14.0% suggests thalassemia) and RBC count (normal/elevated suggests thalassemia) 1, 2, 3, 5
3. Confirm iron status: Measure serum ferritin simultaneously with CBC 2
4. If iron deficient: Provide iron replacement therapy before proceeding with definitive hemoglobin analysis 1, 2
5. Hemoglobin analysis: Perform hemoglobin electrophoresis or HPLC with quantitation of HbA2 and HbF only after excluding or correcting iron deficiency 2
6. For alpha-thalassemia: Molecular testing is necessary for definitive diagnosis 4