A 28-year-old woman from rural Maharashtra presents with fatigue, dyspnea on exertion, and pallor. On examination, she has glossitis and angular cheilitis. Her hemoglobin is 7.2 g/dL with microcytic hypochromic indices. Peripheral blood smear shows target cells and pencil cells. Which is the most appropriate next investigation to confirm iron deficiency anemia?

## Diagnostic Approach to Iron Deficiency Anemia **Key Point:** Serum ferritin and transferrin saturation are the gold standard investigations to confirm iron deficiency and assess iron stores. ### Why Serum Ferritin and Transferrin Saturation? These parameters directly reflect total body iron stores and iron metabolism: - **Serum ferritin** < 12 ng/mL (or < 15 μg/L) is highly specific for iron deficiency - **Transferrin saturation** < 16% confirms impaired iron transport - Both are non-invasive, cost-effective, and widely available - They distinguish iron deficiency from other causes of microcytic anemia (thalassemia, sideroblastic anemia, anemia of chronic disease) ### Diagnostic Algorithm for Microcytic Anemia ```mermaid flowchart TD A[Microcytic Hypochromic Anemia]:::outcome --> B{Clinical + Morphology suggestive of IDA?}:::decision B -->|Yes| C[Serum Ferritin & Transferrin Saturation]:::action C --> D{Ferritin < 12 ng/mL?}:::decision D -->|Yes| E[Iron Deficiency Anemia Confirmed]:::outcome D -->|No| F[Consider other causes]:::action F --> G[Hemoglobin Electrophoresis if thalassemia suspected]:::action F --> H[Iron studies + TIBC if ACD suspected]:::action ``` **High-Yield:** In this patient, the clinical triad of glossitis, angular cheilitis, and microcytic anemia strongly suggests iron deficiency; ferritin/transferrin saturation will confirm it. ### Iron Studies Reference Table | Parameter | Iron Deficiency | Anemia of Chronic Disease | Thalassemia Trait | |-----------|-----------------|---------------------------|-------------------| | **Serum Ferritin** | ↓ (< 12 ng/mL) | ↑ (> 100 ng/mL) | Normal/↑ | | **Transferrin Saturation** | ↓ (< 16%) | Normal/↓ | Normal | | **TIBC** | ↑ | Normal/↓ | Normal | | **RDW** | ↑ | Normal | Normal | | **Mentzer Index (MCV/RBC)** | > 13 | Variable | < 13 | **Clinical Pearl:** Glossitis and angular cheilitis are signs of iron deficiency (Plummer–Vinson syndrome in advanced cases); their presence makes iron studies the logical next step rather than bone marrow examination. **Tip:** Remember the **MNEMONIC: FERRITIN** — Ferritin, Transferrin saturation, Iron stores assessment, Rapid non-invasive test, Iron deficiency confirmation, Transferrin-bound iron, Iron metabolism evaluation, Noninvasive gold standard.