What is the most likely diagnosis for a patient with anemia, low mean corpuscular volume (MCV), and high ferritin?

Anemia with Low MCV and High Ferritin: Anemia of Chronic Disease

The most likely diagnosis is anemia of chronic disease (ACD), also known as anemia of inflammation, particularly when ferritin is >100 μg/L with transferrin saturation <16-20%. 1, 2

Diagnostic Framework

The combination of microcytic anemia (low MCV) with elevated ferritin is characteristic of ACD, though this presentation requires careful interpretation based on inflammatory status:

Key Diagnostic Criteria

In the presence of inflammation:

• Ferritin >100 μg/L + transferrin saturation <16-20% = ACD 3, 1, 2
• This pattern indicates functional iron deficiency where iron is sequestered in storage but unavailable for erythropoiesis due to inflammation-induced hepcidin upregulation 1

Critical caveat: If ferritin is between 30-100 μg/L, suspect combined iron deficiency and ACD 3, 1, 3

Pathophysiology

In ACD, inflammatory cytokines upregulate hepatic hepcidin production, which:

• Reduces iron export from macrophages by degrading ferroportin
• Decreases transferrin saturation and iron delivery to erythroblasts
• Creates functional iron deficiency despite adequate total body iron stores
• Directly inhibits erythropoietin production and bone marrow erythropoiesis 1

Differential Considerations

While microcytic anemia typically suggests iron deficiency 4, the elevated ferritin distinguishes ACD from true iron deficiency anemia, where you would expect:

• Low ferritin (<30 μg/L without inflammation)
• Low iron
• Low transferrin saturation
• Elevated TIBC 4

Other microcytic causes to consider:

• Thalassemia (requires hemoglobin electrophoresis)
• Sideroblastic anemia (rare)
• Lead poisoning (very rare) 4, 1

Essential Workup

To confirm ACD and exclude coexisting conditions, obtain:

1. Inflammatory markers: CRP, ESR (ferritin interpretation depends on inflammatory status) 3, 1
2. Iron studies: Transferrin saturation (expect <16-20% in ACD) 1, 2
3. Reticulocyte count: Should be inappropriately low for degree of anemia 4, 1
4. Consider: Soluble transferrin receptor (sTfR) if available—normal/low in ACD, elevated in true iron deficiency 3

Clinical Context Matters

Look for underlying chronic inflammatory conditions:

• Inflammatory bowel disease (most common extraintestinal manifestation) 3
• Malignancy
• Chronic infections
• Autoimmune diseases
• Chronic kidney disease 1

Important Pitfall

Do not reflexively treat with iron supplementation based solely on low MCV. 5 Ferritin is an acute-phase reactant that rises with inflammation, potentially masking true iron deficiency. However, when ferritin is >100 μg/L with active inflammation, the primary issue is inflammation-mediated iron sequestration, not absolute iron deficiency. Treatment should focus on addressing the underlying inflammatory condition 3.

The lowest MCV reported in pure ACD is approximately 61-67 fL 5, so severe microcytosis does not exclude this diagnosis.