A 5-year-old girl from Kerala presents with mild pallor and jaundice. Her hemoglobin is 9.8 g/dL, MCV 68 fL, and reticulocyte count 4.2%. Peripheral smear shows hypochromic microcytic RBCs with occasional target cells and anisopoikilocytosis. Hemoglobin electrophoresis shows HbA 65%, HbA2 5.2%, and HbF 2%. The child is asymptomatic and has never required transfusion. What is the most likely diagnosis?

## Diagnosis: β-Thalassemia Trait (Heterozygous β-Thalassemia) ### Clinical Presentation This child exhibits the **mild, asymptomatic phenotype** of β-thalassemia trait: - **No transfusion history** — distinguishes from major disease - **Mild pallor and jaundice** — from compensatory hemolysis, not severe anemia - **Asymptomatic** — normal growth and development - **Incidental discovery** — often found on routine screening ### Laboratory Findings | Feature | This Case | β-Thal Trait | β-Thal Major | α-Thal Trait | IDA | |---------|-----------|--------------|--------------|--------------|-----| | **Hb (g/dL)** | 9.8 | 9–11 | 6–8 | 10–12 | 7–10 | | **MCV (fL)** | 68 | 60–70 | 55–65 | 70–80 | 65–75 | | **RBC count** | Not given | ↑↑ (4.5–6.0) | ↑ (3.5–4.5) | Normal | Normal | | **HbA** | 65% | 80–95% | Absent | Normal | Normal | | **HbA2** | 5.2% | **3.5–5.5%** | 2–3% | Normal | Normal | | **HbF** | 2% | 1–3% | 50–90% | <1% | <1% | | **Iron studies** | Not given | Normal | Elevated ferritin | Normal | Low ferritin, ↓TIBC | | **Transfusion need** | None | None | Frequent | None | None | **Key Point:** The **elevated HbA2 (5.2%)** is the **diagnostic hallmark** of β-thalassemia trait. This occurs because one β-globin allele is defective, forcing increased δ-globin chain synthesis (HbA2 = α2δ2). ### Pathophysiology 1. **Heterozygous β-globin mutation** → one functional, one non-functional β-globin allele 2. **Mild reduction in β-globin chains** → slight excess of α-globin chains 3. **Compensatory δ-globin synthesis** → HbA2 rises to 3.5–5.5% (normally 2–3%) 4. **Mild hemolysis** → reticulocytosis (4.2%) and compensatory erythropoiesis 5. **Hypochromic microcytic RBCs** → from reduced hemoglobin per cell 6. **Asymptomatic** → sufficient hemoglobin for normal oxygen delivery ### Hemoglobin Electrophoresis Pattern - **HbA 65%** (reduced but present) — one functional β-globin allele - **HbA2 5.2%** (elevated) — compensatory δ-globin synthesis - **HbF 2%** (normal) — no γ-globin compensation needed **High-Yield:** The **HbA2 level >3.5%** is the **single best discriminator** between β-thalassemia trait and other causes of microcytic anemia (iron deficiency, α-thalassemia trait). ### Mnemonic: THALASSEMIA TRAIT - **T**ransfusion: Not needed - **H**emoglobin: Mildly reduced (9–11 g/dL) - **A**2: Elevated (>3.5%) - **L**ife expectancy: Normal - **A**symptomatic: Usually - **S**mear: Hypochromic microcytic - **S**everity: Mild - **E**lectrophoresis: HbA2 ↑ - **M**CV: Low (60–70 fL) - **I**ron: Normal - **A**lpha: Normal (distinguishes from α-thalassemia) ### Clinical Pearl **β-thalassemia trait is benign in the heterozygous state.** Patients have normal lifespan and no complications. However, genetic counseling is essential: - If both parents are carriers → 25% risk of β-thalassemia major in offspring - Prenatal diagnosis available via chorionic villus sampling or amniocentesis ### Differential Diagnosis: Why Not the Others? **vs. α-Thalassemia Trait:** - α-thalassemia trait has **normal HbA2** (2–3%), not elevated - No Hb Barts on electrophoresis (would see in newborn screening) - MCV is usually higher (70–80 fL vs. 60–70 fL) **vs. Iron Deficiency Anemia:** - IDA has **low ferritin and low TIBC** — this patient's iron studies are normal - IDA has **normal HbA2** — not elevated - RBC count is typically normal or low in IDA; trait has elevated RBC count [cite:Robbins 10e Ch 13]