Anemia of Chronic Disease: A High-Yield USMLE Review

Anemia of chronic disease (ACD), also called anemia of inflammation, is a hypoproliferative anemia driven by chronic inflammatory states such as rheumatoid arthritis and malignancy (including Hodgkin lymphoma). It is the most common cause of normocytic anemia with low reticulocytes, and its iron-study signature—low serum iron, low TIBC, high ferritin—is a favorite exam discriminator against iron deficiency.

Presentation

• Fatigue, the typical nonspecific symptom of anemia
• Occurs in the setting of a chronic inflammatory or malignant illness (e.g., rheumatoid arthritis, Hodgkin lymphoma)
• Usually normocytic (normal MCV), though it can sometimes be microcytic
• Low reticulocyte count reflecting underproduction
• Mild to moderate anemia rather than severe blood loss

Diagnosis

• Iron studies: low serum iron, LOW TIBC, and HIGH ferritin—the classic ACD pattern that distinguishes it from iron deficiency
• CBC: usually normocytic anemia (MCV often normal) with a low reticulocyte count indicating underproduction
• Serum erythropoietin: inappropriately low for the degree of anemia (blunted EPO response)
• When iron deficiency must be excluded in an inflamed patient, order a test unaffected by inflammation—soluble transferrin receptor (sTfR) or the sTfR/log ferritin index (note that transferrin saturation is low in both conditions and cannot reliably discriminate)

Management

• Identify and treat the underlying chronic inflammatory or malignant condition
• Distinguish ACD from concurrent iron deficiency before treating, since it is fundamentally a treatment decision—iron replacement is appropriate only if true iron deficiency is present

High-yield

• Classic iron-study triad: low serum iron, LOW TIBC, HIGH ferritin
• Most common cause of normocytic anemia with low reticulocytes
• Hepcidin traps iron in macrophages → low serum iron but full ferritin stores
• EPO is inappropriately LOW (blunted), not elevated
• Associated with rheumatoid arthritis and Hodgkin lymphoma
• Contrast with iron deficiency: low ferritin, HIGH TIBC, elevated soluble transferrin receptor and RDW

Pitfalls

• Ferritin is an acute-phase reactant—a 'normal' ferritin in an inflamed patient does NOT exclude coexisting iron deficiency; use sTfR or the sTfR/log ferritin index to decide
• Transferrin saturation is low in BOTH ACD and iron deficiency, so it does not reliably distinguish them in an inflamed patient—rely on inflammation-independent tests like sTfR
• Do not assume ACD is always microcytic; it is usually normocytic and only sometimes microcytic, and low iron with low/normal TIBC separates it from thalassemia minor (which has normal iron studies)