A 6-year-old boy from Delhi presents with pallor, hepatosplenomegaly, and recurrent infections. His hemoglobin is 8.5 g/dL with microcytic indices. Serum ferritin is markedly elevated at 450 ng/mL, and transferrin saturation is 65%. Peripheral blood smear shows target cells. Which investigation is most appropriate to determine the underlying cause of secondary iron overload?

Explanation

## Secondary Iron Overload in Microcytic Anemia **Key Point:** In a child with microcytic anemia, hepatosplenomegaly, elevated ferritin, and high transferrin saturation, hemoglobin electrophoresis is the most appropriate next investigation to identify the underlying hemoglobinopathy causing secondary iron overload. ### Clinical Context: Secondary Hemochromatosis Secondary iron overload occurs in chronic hemolytic anemias requiring repeated transfusions. In this Indian pediatric patient, **β-thalassemia major** is the most likely diagnosis: - Microcytic hypochromic anemia - Target cells on blood smear - Hepatosplenomegaly (from extramedullary hematopoiesis and iron deposition) - Elevated ferritin and transferrin saturation - Recurrent infections (from splenic dysfunction and iron-induced immunosuppression) ### Diagnostic Pathway for Secondary Iron Overload ```mermaid flowchart TD A[Microcytic Anemia + Hepatosplenomegaly + High Ferritin]:::outcome --> B{Clinical suspicion for hemoglobinopathy?}:::decision B -->|Yes| C[Hemoglobin Electrophoresis]:::action C --> D{Abnormal Hb pattern?}:::decision D -->|β-Thalassemia| E[Confirm with Genetic Testing]:::action D -->|Sickle Cell or other| F[Specific diagnosis confirmed]:::outcome B -->|No| G[Consider other causes of secondary iron overload]:::action E --> H[Iron chelation therapy + transfusion management]:::action ``` **High-Yield:** Hemoglobin electrophoresis is the **first-line investigation** to identify the underlying hemoglobinopathy in secondary iron overload. It distinguishes β-thalassemia, α-thalassemia, sickle cell disease, and other hemoglobinopathies. ### Iron Overload Investigations: When to Use Each | Investigation | Purpose | When to Order | |---|---|---| | **Hemoglobin Electrophoresis** | Identify hemoglobinopathy causing chronic hemolysis | First-line for suspected thalassemia/sickle cell | | **Genetic Testing (β-globin mutations)** | Confirm diagnosis and assess severity | After abnormal electrophoresis | | **Bone Marrow Iron Stain (Prussian blue)** | Assess iron stores in marrow | Rarely needed; mainly for research | | **Serum Transferrin Receptor** | Assess erythropoietic activity | Distinguish iron deficiency from anemia of chronic disease | | **Liver Biopsy** | Quantify hepatic iron; assess fibrosis | Only if cirrhosis suspected; not diagnostic | | **MRI T2* (heart, liver)** | Non-invasive iron quantification | After diagnosis confirmed; for monitoring | **Clinical Pearl:** The combination of **target cells + hepatosplenomegaly + high ferritin in a child** is pathognomonic for β-thalassemia major. Hemoglobin electrophoresis will show HbF and HbA₂ elevation with absent or markedly reduced HbA. **Mnemonic: THALASSEMIA DIAGNOSIS** — **T**arget cells, **H**emoglobin electrophoresis (first test), **A**lpha/Beta globin mutations, **L**iver iron (MRI later), **A**nemia (chronic, microcytic), **S**plenomegaly, **S**econdary iron overload, **E**lectrophoresis shows HbF/HbA₂, **M**utations confirm, **I**ron chelation needed, **A**ssess cardiac/hepatic iron.