A 52-year-old man presents with a 3-month history of fatigue and dyspnea. Laboratory findings: Hb 8.9 g/dL, MCV 78 fL, MCH 24 pg, RBC count 5.8 × 10^12/L, serum iron 95 µg/dL (normal 60–170), ferritin 320 ng/mL (normal 12–200), TIBC 280 µg/dL (normal 250–425). Peripheral blood smear shows microcytic RBCs with target cells and occasional nucleated RBCs. What is the most appropriate next step in management?

Explanation

## Clinical Context This patient presents with **microcytic anemia**, but the biochemical iron profile is **NOT consistent with iron deficiency**: - Normal serum iron (95 µg/dL) - **Elevated ferritin** (320 ng/mL) — rules out IDA - Normal TIBC (280 µg/dL) - **High RBC count** (5.8 × 10^12/L) — disproportionately high for the degree of anemia - **Nucleated RBCs** on smear — suggests dysplasia or hemolysis This pattern is **NOT iron deficiency**. The differential diagnosis for microcytic anemia without iron deficiency includes: 1. **Thalassemia trait** (β-thalassemia heterozygote) 2. Anemia of chronic disease 3. Sideroblastic anemia 4. Lead poisoning ## Rationale for Correct Answer **Key Point:** When microcytic anemia occurs **without iron deficiency** (normal/high iron, elevated ferritin), the next step is **hemoglobin electrophoresis** to identify hemoglobinopathies, particularly **thalassemia trait**. **High-Yield:** The **Mentzer Index** helps differentiate thalassemia trait from IDA: $$\text{Mentzer Index} = \frac{MCV}{RBC \text{ count}} = \frac{78}{5.8} = 13.4$$ - **< 13** = suggests thalassemia trait - **> 13** = suggests iron deficiency This patient's index (13.4) is borderline, but combined with **normal iron and elevated ferritin**, thalassemia trait is highly likely. ## Diagnostic Approach **Hemoglobin electrophoresis** will show: - **β-thalassemia trait**: elevated HbA2 (3.5–7%) and/or elevated HbF (1–3%) - **α-thalassemia trait**: normal HbA2 and HbF (requires genetic testing) ## Why Not Iron Therapy? - **Oral iron is contraindicated** in thalassemia trait; iron overload worsens hemolysis and organ damage - Ferritin is already elevated, indicating iron accumulation - Giving iron to a thalassemia patient causes secondary hemochromatosis **Clinical Pearl:** Thalassemia trait is often asymptomatic and discovered incidentally. It requires **no treatment** but genetic counseling for reproductive planning. Misdiagnosis as IDA and inappropriate iron supplementation causes harm. [cite:Harrison 21e Ch 98; KD Tripathi 8e Ch 12]