A 65-year-old man with long-standing rheumatoid arthritis has Hb 10.2 g/dL, MCV 78 fL. Which laboratory finding best distinguishes anemia of chronic disease from iron deficiency anemia?

• A Serum iron
• B Transferrin saturation
• C Total iron binding capacity
• D Serum ferritin ✓

Explanation

Serum ferritin is the most reliable discriminator. In anemia of chronic disease, ferritin is normal or elevated because it is an acute phase reactant, despite low serum iron. In iron deficiency, ferritin is low. Both conditions show low serum iron and low transferrin saturation. TIBC is high in iron deficiency but low or normal in chronic disease, though ferritin is the single best test.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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