A 42-year-old woman presents with fatigue and dyspnea on exertion. On examination, she has pallor and glossitis. Her hemoglobin is 8.2 g/dL with MCV 62 fL. Which investigation is most specific for confirming iron deficiency anemia?

Explanation

## Confirmatory Investigation for Iron Deficiency Anemia ### Why Bone Marrow Iron Staining is Gold Standard **Key Point:** Prussian blue (Prussian blue) staining of bone marrow aspirate is the most specific and direct test for assessing iron stores. Absence of iron in macrophages is pathognomonic for iron deficiency. **High-Yield:** While serum ferritin and TIBC are useful screening tests, they can be falsely elevated in inflammation, infection, and malignancy. Bone marrow examination directly visualizes iron stores and rules out other causes of microcytic anemia (thalassemia, sideroblastic anemia). ### Investigation Hierarchy for Iron Deficiency | Investigation | Sensitivity | Specificity | Limitation | |---|---|---|---| | Serum ferritin | High | Low (↑ in inflammation) | Acute phase reactant | | Serum iron + TIBC | Moderate | Moderate | Diurnal variation, affected by diet | | Transferrin saturation | Good | Good | Still affected by inflammation | | Bone marrow iron stain | Very high | Very high (gold standard) | Invasive, not routine | **Clinical Pearl:** In clinical practice, iron studies (ferritin + TIBC + serum iron) are first-line because they are non-invasive. Bone marrow examination is reserved for: - Diagnostic uncertainty (e.g., concurrent inflammation) - Microcytic anemia not responding to iron therapy - Need to exclude other causes (thalassemia, sideroblastic anemia) **Mnemonic: STAIN** — Specific Test for iron Absence IN macrophages (Prussian blue stain = gold standard)