A 28-year-old woman from rural Maharashtra presents with pallor and dyspnea on exertion. Laboratory investigations show Hb 7.2 g/dL, MCV 62 fL, serum iron 45 µg/dL, TIBC 420 µg/dL, and ferritin 12 ng/mL. Which single feature best distinguishes iron deficiency anemia from anemia of chronic disease in this patient?

Explanation

## Discriminating Iron Deficiency Anemia from Anemia of Chronic Disease ### Key Laboratory Distinction **Key Point:** The combination of **low serum ferritin AND elevated TIBC** is the single best discriminator between iron deficiency anemia (IDA) and anemia of chronic disease (ACD). ### Comparative Table | Feature | Iron Deficiency Anemia | Anemia of Chronic Disease | |---------|------------------------|---------------------------| | **Serum Ferritin** | ↓ Low (<30 ng/mL) | ↑ Normal or elevated (>100 ng/mL) | | **TIBC** | ↑ Elevated (>360 µg/dL) | ↓ Low or normal (<300 µg/dL) | | **Serum Iron** | ↓ Low | ↓ Low | | **Transferrin Saturation** | ↓ Low (<16%) | ↓ Low (<16%) | | **MCV** | ↓ Microcytic | Normal or slightly ↓ | | **RDW** | ↑ Elevated | Normal | ### Pathophysiology **High-Yield:** In IDA, the body has depleted iron stores (low ferritin) and responds by upregulating hepcidin-independent iron absorption, causing TIBC to rise as the iron transport system attempts to maximize iron uptake. In ACD, hepcidin is elevated due to inflammation, blocking iron absorption and recycling, resulting in **low TIBC** despite adequate or elevated body iron stores. ### Clinical Pearl Why ferritin alone is insufficient: Ferritin is an acute-phase reactant and can be falsely elevated in chronic inflammation, infection, or malignancy. TIBC is NOT an acute-phase reactant, making the **ferritin-TIBC pattern** the most reliable discriminator. ### Mnemonic **"IDA = Hungry for Iron"** — IDA shows high TIBC (the transferrin "appetite" is high because stores are empty); **"ACD = Locked Away"** — ACD shows low TIBC (hepcidin locks iron away despite adequate stores). [cite:Harrison 21e Ch 99]