Anemia of chronic disease

Pathophysiology - Chronic Inflammation's Iron Fist

• Central Mediator: Chronic inflammation (autoimmune, infectious, malignant) ↑ key cytokines like IL-6.
• Hepcidin Surge: IL-6 triggers the liver to release hepcidin, the master iron regulator.
• Iron Sequestration: Hepcidin acts as an "iron gatekeeper":
  • Blocks ferroportin channels in the gut, ↓ dietary iron absorption.
  • Traps iron within macrophages of the reticuloendothelial system (RES).
• Result: Functional iron deficiency. Despite adequate body stores (↑ ferritin), iron is unavailable for erythropoiesis, leading to ↓ heme synthesis.
• Other Factors: Blunted erythropoietin (EPO) response.

⭐ Despite low serum iron, ferritin levels are paradoxically normal or ↑ because it's an acute phase reactant and reflects trapped iron stores. This is a key diagnostic clue.

Diagnosis & Labs - Cracking the Code

• CBC/Blood Smear: Initially normocytic, normochromic anemia (MCV 80-100 fL); can become microcytic over time.
• Iron Studies Panel: The key to diagnosis.
  • ↓ Serum Iron
  • ↓ Total Iron-Binding Capacity (TIBC)
  • ↑ or Normal Serum Ferritin (acute phase reactant)
  • ↓ Transferrin Saturation (<20%)
• Advanced Markers:
  • ↑ Hepcidin (confirms pathophysiology)
  • Normal soluble transferrin receptor (sTfR)

⭐ Serum ferritin, an acute-phase reactant, is characteristically normal or elevated in ACD, contrasting sharply with its depletion in pure iron deficiency anemia.

Differential Diagnosis - Anemia Imposters

• Iron Deficiency Anemia (IDA): The most critical differential. Overlaps with early ACD (normocytic).
• Thalassemia: Presents with microcytic anemia but with normal or ↑ iron stores.
• Sideroblastic Anemia: Can be microcytic; characterized by ring sideroblasts in bone marrow.

⭐ The soluble transferrin receptor (sTfR) level is normal in ACD but elevated in IDA. The sTfR/log(ferritin) index is highly specific for differentiating IDA from ACD.

Management - Treating the Cause

• Primary Goal: Resolve the underlying chronic disease (e.g., infection, autoimmune condition, malignancy).
• Iron Supplementation: Only if coexistent iron deficiency is confirmed (↓ ferritin). IV iron is often preferred due to poor oral absorption from hepcidin block.
• Erythropoiesis-Stimulating Agents (ESAs): Consider for specific conditions like CKD or myelosuppressive chemotherapy if anemia is symptomatic.

⭐ ESAs (e.g., epoetin alfa) require adequate iron stores to be effective and may increase the risk of thrombosis and hypertension.

High-Yield Points - ⚡ Biggest Takeaways

• ACD is a normocytic, normochromic anemia, but can become microcytic over time.
• It is driven by inflammatory cytokines (e.g., IL-6) in chronic diseases, which stimulate ↑ hepcidin production.
• Hepcidin blocks iron release from macrophages and reduces gut absorption, leading to functional iron deficiency.
• Key lab profile: ↓ serum iron, ↓ TIBC, and normal or ↑ ferritin (an acute-phase reactant).
• Bone marrow shows adequate iron stores, unlike in true iron deficiency.
• Management focuses on treating the underlying condition.