Anemia of chronic disease (ACD)—also called anemia of inflammation—is one of those Step 1 favorites because it looks like iron deficiency at first glance, but the mechanism (and labs) are the exact opposite story. If you can explain why the body hides iron during inflammation, you can usually nail the question.
Where This Fits (Step 1 Mental Map)
ACD is typically a normocytic anemia early, and can become microcytic later. It’s classically associated with chronic inflammatory states and has a very characteristic iron panel.
First Aid cross-reference (typical placement):
- Hematology → Anemias → Microcytic anemias (and/or Normocytic anemias), “Anemia of chronic disease”
- Immunology/Pathology → Cytokines & acute phase reactants (IL-6, hepcidin)
Definition (What ACD Actually Is)
Anemia of chronic disease is a hypoproliferative anemia caused by chronic inflammation leading to:
- impaired iron availability to developing RBCs (iron “sequestration”)
- decreased RBC production (less erythropoiesis)
- shortened RBC lifespan (mild hemolysis via macrophage activity)
Key idea: Total body iron is usually normal or increased, but it’s trapped in macrophages and unavailable to the marrow.
High-Yield Etiologies (“What Counts as Chronic Disease?”)
Think “inflammation” broadly:
- Chronic infections
- TB, HIV, endocarditis, osteomyelitis
- Autoimmune/inflammatory diseases
- Rheumatoid arthritis, IBD, SLE
- Malignancy
- Especially solid tumors and hematologic cancers
- Chronic kidney disease
- Often overlaps (ACD + ↓EPO)
USMLE vibe: If the stem gives you chronic inflammatory symptoms + low iron + high ferritin, your reflex should be ACD.
Pathophysiology (The Story You Must Be Able to Tell)
1) IL-6 → Hepcidin goes up (the central mechanism)
Inflammation increases IL-6, which stimulates the liver to make hepcidin.
Hepcidin inhibits ferroportin, the iron exporter on:
- enterocytes (gut)
- macrophages (reticuloendothelial system)
Result:
- ↓ iron absorption from the gut
- ↓ iron release from macrophages
- ↓ iron delivery to bone marrow
Net effect: functional iron deficiency despite adequate stores.
2) Erythropoiesis is suppressed
Inflammatory cytokines (e.g., IL-1, TNF-α) decrease:
- EPO production
- marrow responsiveness to EPO
3) RBC lifespan is shortened
Inflammation increases macrophage-mediated RBC clearance (usually mild).
Clinical Presentation (What You’ll See in a Stem)
Most patients have symptoms of the underlying condition and mild-to-moderate anemia.
Common findings:
- Fatigue, weakness, exertional dyspnea
- Often no specific iron-deficiency signs (e.g., pica, koilonychia) unless concurrent iron deficiency exists
- May have systemic inflammation clues:
- fever, weight loss, night sweats
- chronic joint pain (RA), GI symptoms (IBD), etc.
Severity: usually mild/moderate (often Hb ~8–11 g/dL), but can vary.
Diagnosis: The High-Yield Lab Pattern
CBC / smear
- MCV: normal early; can be low later
- Reticulocyte count: low (hypoproliferative)
- Smear: usually nonspecific (may be normocytic, normochromic)
Iron studies (core Step 1 content)
| Test | Anemia of Chronic Disease | Iron Deficiency Anemia (contrast) |
|---|---|---|
| Serum iron | ↓ | ↓ |
| Ferritin | ↑ (acute phase reactant; iron stores high) | ↓ |
| TIBC (transferrin) | ↓ | ↑ |
| Transferrin saturation | ↓ | ↓ |
| Hepcidin | ↑ | ↓ |
The money combo for ACD:
Low iron + low TIBC + high ferritin
Why ferritin matters
Ferritin is both:
- an iron storage protein, and
- an acute phase reactant
So in inflammation, ferritin goes up even if circulating iron is low.
Step-Style Differentiation: ACD vs Iron Deficiency vs Thalassemia
If you’re torn between common microcytic causes, use this quick sorting:
- ACD: ↓ iron, ↓ TIBC, ↑ ferritin
- Iron deficiency: ↓ iron, ↑ TIBC, ↓ ferritin
- Thalassemia: normal iron studies; target cells; very low MCV relative to anemia severity
Extra HY clue: In ACD, the marrow has iron available in storage but won’t release it; in iron deficiency, iron stores are truly depleted.
Treatment (Do Not Just Give Iron Blindly)
1) Treat the underlying disease
This is the definitive management:
- control inflammation/infection
- treat malignancy
- manage autoimmune disease activity
2) EPO-stimulating agents (selected cases)
Consider in:
- CKD-associated anemia
- some chronic inflammatory states with severe symptoms
Step pearl: CKD can cause anemia via ↓EPO, but chronic inflammation can still contribute via ↑hepcidin—so you may see mixed mechanisms.
3) Iron therapy: only if true deficiency is present
Because iron is being sequestered, oral iron alone often doesn’t fix ACD.
Give iron if:
- labs also suggest true iron deficiency (e.g., low ferritin in a non-inflammatory context, or other supportive testing)
- there is ongoing blood loss (e.g., malignancy + GI bleed)
4) Transfusion (rare, symptomatic/severe)
Used for:
- significant symptoms
- very low Hb
- acute need (bridge while treating underlying cause)
High-Yield Associations & Board Traps
“Inflammation hides iron”
A classic Step 1 explanation:
- The body “locks away” iron during inflammation to reduce microbial access to iron.
- This protective response becomes maladaptive in chronic inflammation.
ACD is often normocytic
If you see normocytic anemia with low retic in someone with chronic inflammatory disease, think ACD even before you see the iron panel.
Ferritin is the trap
Students often misread low serum iron and jump to iron deficiency. On boards, ferritin saves you:
- ACD: ferritin high
- IDA: ferritin low
TIBC goes the opposite direction
- ACD: the liver decreases transferrin → low TIBC
- IDA: liver increases transferrin to scavenge iron → high TIBC
Mixed pictures are common clinically
Real patients can have RA (ACD) plus menorrhagia (iron deficiency).
Step questions usually keep it clean—but if they don’t, look for:
- unexpectedly low ferritin (true iron deficiency)
- very high RDW (more supportive of iron deficiency than isolated ACD)
Quick “If You Remember Only 5 Things” Checklist
- ACD = anemia of inflammation (IL-6 driven)
- Hepcidin ↑ → ferroportin inhibited → iron trapped in macrophages, less absorbed in gut
- Low serum iron + low TIBC + high ferritin
- Usually normocytic, low retic
- Treat the cause; consider EPO in CKD; iron only if truly deficient