In iron deficiency anemia, the serum ferritin level is typically reduced. Which of the following best explains why ferritin is a reliable marker of total body iron stores?

Explanation

## Ferritin as a Marker of Iron Stores **Key Point:** Ferritin is the primary intracellular iron storage protein. Its serum concentration reflects total body iron stores because ferritin synthesis is tightly regulated by intracellular iron levels. ### Regulation of Ferritin Synthesis 1. **Iron-Responsive Elements (IREs)**: Ferritin mRNA contains a 5' IRE in its untranslated region 2. **Iron Regulatory Proteins (IRPs)**: When intracellular iron is low, IRPs bind to the IRE and block ferritin translation 3. **Iron-Dependent Translation**: When iron is abundant, IRPs release from IRE, allowing ferritin mRNA translation 4. **Proportional Relationship**: Serum ferritin levels correlate with total body iron stores (both storage and functional iron) ### Ferritin Levels in Clinical States | Clinical State | Serum Ferritin | Total Body Iron | Interpretation | |---|---|---|---| | Iron deficiency | < 15 μg/L | Depleted | Reliable marker of depletion | | Normal | 30–300 μg/L (M); 15–200 μg/L (F) | Normal | Reflects stores | | Iron overload | > 300 μg/L | Excess | Indicates hemochromatosis | | Inflammation/Infection | ↑↑ | May be normal | False elevation (acute phase reactant) | **High-Yield:** Ferritin is an acute phase reactant — it rises in infection, malignancy, and inflammation independent of iron status. This is a classic NEET PG trap: normal or high ferritin does NOT exclude iron deficiency in an inflamed patient. **Mnemonic:** **IRE-IRP Axis** — **I**ron **R**esponsive **E**lements bind **I**ron **R**egulatory **P**roteins to control ferritin and transferrin receptor translation inversely. **Clinical Pearl:** In anemia of chronic disease, ferritin is elevated (inflammation) while iron stores may be normal or increased — ferritin becomes unreliable. Use bone marrow iron staining or soluble transferrin receptor (sTfR) to clarify.