Iron Deficiency Anemia vs Anemia of Chronic Disease on Board Exams

Ferritin and total iron binding capacity (TIBC) separate these two anemias on almost every board question. Iron deficiency anemia has a low ferritin and a high TIBC, because the body has run out of stored iron and is making more transferrin to find some. Anemia of chronic disease has a normal or high ferritin and a low TIBC, because inflammation locks plenty of iron inside macrophages. Serum iron is low in both, so it can't be the tiebreaker.

Why do iron deficiency and anemia of chronic disease look alike?

Both anemias starve the red cell precursors in the marrow of iron. The marrow can't build enough hemoglobin, so it makes fewer red cells, and the reticulocyte count stays low for the degree of anemia. Both can be microcytic. Both lower the serum iron. A stem that only gives you a hemoglobin, an MCV, and a serum iron hasn't given you enough to choose.

The difference is where the iron went. In iron deficiency, the iron is gone. Blood loss, poor absorption, or high demand has emptied the body's stores, and there's nothing left in the marrow or the macrophages. In anemia of chronic disease, the iron is still in the body. It's trapped inside macrophages and liver cells, where the marrow can't reach it.

That one idea predicts every lab on the panel. Empty stores give a low ferritin. Full but locked stores give a normal or high ferritin. Once you hold that picture, you don't have to memorize the table as a list of arrows.

How does hepcidin cause anemia of chronic disease?

Hepcidin is the hormone behind anemia of chronic disease. The liver makes it, and inflammatory cytokines, mainly interleukin-6 (IL-6), push the liver to make more. Hepcidin binds ferroportin, the only known channel that moves iron out of cells, and causes it to be pulled inside and degraded.

Losing ferroportin has two effects. Duodenal enterocytes absorb dietary iron but can't export it into the blood, so the iron is lost when those cells slough off. Macrophages that recycle iron from old red cells can't release it either, so the iron piles up inside them. The serum iron falls, the ferritin rises, and the marrow gets very little.

Inflammation adds two more problems. Cytokines blunt the kidney's erythropoietin (EPO) response, and they shorten red cell survival. The result is usually a mild to moderate anemia that tracks the activity of the underlying disease.

From an evolutionary standpoint, this makes sense. Bacteria need iron to grow, so hiding iron during infection is a defense. Anemia is the cost. Weiss, Ganz, and Goodnough's 2019 review in Blood uses the newer name "anemia of inflammation," and you'll see both terms in question banks.

What do the iron studies show in each?

This is the table to know cold. It's built for elimination: find one lab that doesn't fit, and the other answer is gone.

Reading the panel in the right order

Start with ferritin. Ferritin is the storage form of iron, so a low ferritin means iron deficiency. A ferritin under 30 ng/mL is a common cutoff, and the American Gastroenterological Association's 2020 guideline uses under 45 ng/mL in an anemic patient. On a board question, a single-digit or teens ferritin is iron deficiency anemia until proven otherwise.

Next, look at TIBC. TIBC is an indirect measure of transferrin, the protein that carries iron in the blood. When stores run low, the liver makes more transferrin, so TIBC rises in iron deficiency. Inflammation does the opposite and lowers transferrin, so TIBC falls in anemia of chronic disease.

Then check transferrin saturation, which is serum iron divided by TIBC. It's low in iron deficiency because the numerator is small and the denominator is big. It can also be low in anemia of chronic disease, so it confirms rather than decides.

The ferritin trap

Ferritin is an acute phase reactant. Infection, inflammation, cancer, and liver disease all raise it on their own. That means a normal ferritin in a patient with active rheumatoid arthritis doesn't rule out iron deficiency. A patient can have both problems at once, and the ferritin will look better than the iron stores really are.

Iron deficiency anemia: the stores are empty

Board settings and causes of iron deficiency anemia

Iron deficiency anemia is the most common anemia in the world. The cause depends on who the patient is, and the stem almost always tells you.

• Menstruating women and pregnancy. Menstrual blood loss and the iron demands of pregnancy are the classic causes in young women.
• An adult man or a postmenopausal woman. Assume gastrointestinal blood loss. Colon cancer is the answer they want you to rule out, and right-sided colon cancer is the classic one to bleed slowly and present as iron deficiency anemia.
• Infants and toddlers. Excess cow's milk is the classic cause in a toddler, because it's low in iron and can cause occult intestinal blood loss.
• Malabsorption. Celiac disease, gastric bypass, and partial gastrectomy cut duodenal absorption. Iron deficiency that doesn't respond to oral iron should make you think of celiac disease.
• Hookworm. Necator americanus and Ancylostoma duodenale attach to the small bowel wall and cause chronic blood loss. Expect a traveler or a patient from an endemic area, sometimes with eosinophilia.
• Chronic NSAID use. Gastric and duodenal ulcers can bleed slowly for months without a dramatic presentation.

Exam findings that point to iron deficiency

Some findings show up only in iron deficiency, and stems use them as giveaways. Koilonychia (spoon-shaped nails), angular cheilitis, glossitis, and pica are the classic ones. Pagophagia, a craving to chew ice, is a specific form of pica. Plummer-Vinson syndrome adds esophageal webs and dysphagia to iron deficiency anemia, and it raises the risk of esophageal squamous cell carcinoma.

The smear shows small, pale red cells with a wider area of central pallor. Pencil cells (elongated, thin red cells) are a classic iron deficiency finding. The RDW is high because new red cells come out smaller than the older ones.

Treating iron deficiency anemia and the next-step question

Oral iron is the first-line board answer for most patients. The reticulocyte count should rise within about a week, and that rise is how the stem tells you the diagnosis was right. Intravenous iron is the answer when the patient can't absorb or tolerate oral iron, as after gastric bypass or in active inflammatory bowel disease.

Hepcidin shows up here too. Stoffel and colleagues showed in 2017 that an oral iron dose raises hepcidin for about 24 hours, which lowers absorption of the next day's dose. That's why alternate-day dosing has gained ground. Boards rarely test the schedule, but they do test the mechanism.

The next-step question matters more than the treatment question. In an older man or a postmenopausal woman with new iron deficiency anemia, the answer is a GI workup, usually colonoscopy and upper endoscopy. Giving iron and sending the patient home misses the cancer the stem was built around.

Anemia of chronic disease: the iron is locked away

Board settings and causes of anemia of chronic disease

Anemia of chronic disease follows any long-standing inflammatory, infectious, or malignant process. The stem gives you the chronic disease, sometimes in the past medical history and sometimes in a single clue.

• Autoimmune disease. Rheumatoid arthritis and systemic lupus erythematosus are the classic settings.
• Chronic infection. Tuberculosis, osteomyelitis, infective endocarditis, and HIV all qualify.
• Malignancy. Solid tumors and lymphomas both cause it. A patient with Hodgkin lymphoma and B symptoms can present with anemia of chronic disease.
• Inflammatory bowel disease. Crohn's disease and ulcerative colitis can cause anemia of chronic disease, iron deficiency, or both at once, which makes IBD a favorite mixed-picture stem. The Crohn's vs ulcerative colitis guide covers the rest of that differential.
• Chronic kidney disease. The main driver is low EPO from the damaged kidney, with inflammation and iron restriction on top.

Treating anemia of chronic disease

Treat the underlying disease. When rheumatoid arthritis is controlled, the IL-6 drops, hepcidin falls, and the anemia improves. Oral iron doesn't help much, because high hepcidin blocks its absorption at the duodenum.

Erythropoiesis-stimulating agents, such as recombinant EPO, are the board answer for anemia of chronic kidney disease and for some patients with cancer-related anemia. They work poorly if iron stores are low, so iron status is checked first. The KDIGO 2012 guideline suggests a trial of iron in CKD when transferrin saturation is 30% or lower and ferritin is 500 ng/mL or lower.

When the patient has both

Real patients and harder board questions combine the two. A patient with rheumatoid arthritis who takes NSAIDs every day can have anemia of chronic disease from the arthritis and iron deficiency from a bleeding ulcer.

The labs land in between. Ferritin looks normal because inflammation is propping it up, but it's lower than you'd expect for the amount of inflammation. Weiss and Goodnough's 2005 NEJM review lists a ferritin under 100 ng/mL in an inflamed patient, with a low transferrin saturation, as a sign that true iron deficiency is also present.

The soluble transferrin receptor is the tiebreaker. Iron-starved red cell precursors make more transferrin receptors, so the soluble receptor rises in iron deficiency. Inflammation doesn't raise it, so it stays normal in pure anemia of chronic disease. A high soluble transferrin receptor in an inflamed patient means iron deficiency is in the mix. If the stem offers a bone marrow biopsy, absent stainable iron settles it.

The other microcytic anemias that show up as distractors

Microcytic anemia questions usually offer iron deficiency, anemia of chronic disease, thalassemia, sideroblastic anemia, and lead poisoning as the answer choices. The iron studies eliminate most of them in one pass.

The Mentzer index is the MCV divided by the red cell count in millions per microliter. Under 13 favors thalassemia trait, because the marrow makes many small cells. Over 13 favors iron deficiency, because the marrow makes fewer cells. When the iron studies come back normal in a microcytic patient, think thalassemia first.

Three patients, same complaint: working the stems

Here are three example stems built to show the split. Each patient presents with fatigue and a hemoglobin around 10 g/dL.

Patient 1. A 67-year-old man has 3 months of fatigue and exertional dyspnea. He has no history of chronic illness. Hemoglobin is 9.6 g/dL, MCV is 72 fL, RDW is high, ferritin is 6 ng/mL, and TIBC is high. Stool is positive for occult blood.

The ferritin and TIBC make this iron deficiency anemia. The real question is why an older man is iron deficient, and the answer is colon cancer until proven otherwise. The next step is a GI workup with colonoscopy and upper endoscopy.

Patient 2. A 54-year-old woman has rheumatoid arthritis with morning stiffness and swollen metacarpophalangeal joints. Hemoglobin is 10.4 g/dL, MCV is 84 fL, RDW is normal, ferritin is 310 ng/mL, TIBC is low, and serum iron is low. Her ESR and CRP are elevated.

The high ferritin and low TIBC point to anemia of chronic disease. The low serum iron is the trap, because it pushes students toward iron deficiency. Oral iron is the wrong answer here. Better control of her rheumatoid arthritis is what improves the anemia.

Patient 3. A 59-year-old man with rheumatoid arthritis takes naproxen every day. He now has dark stools. Hemoglobin is 9.1 g/dL, MCV is 77 fL, ferritin is 62 ng/mL, transferrin saturation is 7%, and the soluble transferrin receptor is elevated.

His ferritin is in the normal range, but it's low for an inflamed patient, and the soluble transferrin receptor is high. That's combined anemia of chronic disease and iron deficiency anemia, with an NSAID ulcer as the likely bleeding source. The next step is upper endoscopy.

If you want more worked stems like these, the free Skool community has a video library of question breakdowns.

Stem clues that crack these questions fast

The clues I look for in every question are age, acuity, unusual findings, matching timelines, laterality, labs and imaging, and the question part. Here's how they apply to this topic.

1. Age. A toddler drinking a lot of cow's milk, a menstruating woman, and a 65-year-old man are three different iron deficiency stories. In the older adult, think colon cancer.
2. Matching timelines. Anemia that develops over months alongside a chronic inflammatory disease points to anemia of chronic disease. Anemia that tracks heavy periods or months of NSAID use points to blood loss.
3. Unusual findings. Koilonychia, pagophagia, and dysphagia from esophageal webs belong to iron deficiency. Stems rarely mention a craving for ice for no reason.
4. Labs are king. Read ferritin first and TIBC second. Low ferritin with high TIBC is iron deficiency. Normal or high ferritin with low TIBC is anemia of chronic disease. Normal iron studies in a microcytic patient point to thalassemia.
5. The question part. "Most likely diagnosis," "most appropriate next step," and "most likely cause" ask different things. In an older adult with iron deficiency, the next step is usually endoscopy, not iron.

When two answers both look right on an iron question, the guide to choosing between two answers on COMLEX walks through how to break the tie.

Common board pitfalls and how to avoid them

Pitfall 1 is using serum iron to decide. Serum iron is low in both. It narrows the field to these two, but ferritin and TIBC choose between them.

Pitfall 2 is trusting a normal ferritin in an inflamed patient. Ferritin rises with inflammation. A ferritin under 100 ng/mL with a low transferrin saturation in active disease suggests coexisting iron deficiency.

Pitfall 3 is treating iron deficiency without finding the cause. In an adult man or a postmenopausal woman, the stem is about GI blood loss. Iron alone is the wrong next step.

Pitfall 4 is giving oral iron for anemia of chronic disease. High hepcidin blocks absorption, so oral iron does little. Treat the underlying disease.

Pitfall 5 is assuming every microcytic anemia is iron deficiency. Normal iron studies point to thalassemia trait. High serum iron and high ferritin with ringed sideroblasts point to sideroblastic anemia.

Pitfall 6 is calling anemia of chronic disease normocytic every time. It's usually normocytic, but long-standing disease can make it microcytic. Let the ferritin and TIBC decide, not the MCV.

Frequently asked questions about iron deficiency anemia vs anemia of chronic disease

How do you tell iron deficiency anemia from anemia of chronic disease on labs?

Look at ferritin and TIBC. Iron deficiency anemia has a low ferritin, often under 30 ng/mL, and a high TIBC, because the iron stores are empty and the liver makes more transferrin. Anemia of chronic disease has a normal or high ferritin and a low TIBC, because inflammation traps iron in macrophages and lowers transferrin. Serum iron is low in both, so it doesn't separate them. The soluble transferrin receptor is high in iron deficiency and normal in anemia of chronic disease.

Why is ferritin high in anemia of chronic disease?

Ferritin is the storage form of iron, and it's also an acute phase reactant. In anemia of chronic disease, hepcidin blocks iron from leaving macrophages, so stored iron builds up and ferritin rises. Inflammation raises ferritin directly on top of that. This is why a normal ferritin in an inflamed patient doesn't rule out iron deficiency. A ferritin under 100 ng/mL with a low transferrin saturation in that setting suggests both problems are present.

What does hepcidin do in anemia of chronic disease?

Hepcidin is made by the liver, and IL-6 from inflammation increases its production. It binds ferroportin, the channel that exports iron from cells, and causes it to be degraded. Duodenal cells can no longer pass absorbed iron into the blood, and macrophages can no longer release recycled iron. Serum iron falls while stored iron rises. The marrow is left without enough iron to make hemoglobin, even though the body holds plenty.

Is anemia of chronic disease microcytic or normocytic?

It's usually normocytic, with a normal RDW. Long-standing or severe disease can make it mildly microcytic, which is why the MCV alone doesn't separate it from iron deficiency. Iron deficiency anemia starts normocytic and becomes microcytic as stores run out, with a high RDW. On a board question, use ferritin and TIBC to decide, and use the MCV only to narrow the differential to microcytic causes.

What is the next step for iron deficiency anemia in an older adult?

Find the source of blood loss. In a man or a postmenopausal woman with new iron deficiency anemia, the board answer is a GI evaluation, usually colonoscopy and upper endoscopy, because colon cancer has to be ruled out. Right-sided colon cancer classically bleeds slowly and presents this way. Iron replacement is part of treatment, but iron alone is the wrong next step when the stem is built around an occult bleed.

Can a patient have both iron deficiency and anemia of chronic disease?

Yes, and harder board questions use this. A patient with rheumatoid arthritis or inflammatory bowel disease can bleed from the gut while inflammation raises ferritin. The ferritin may look normal but sits lower than expected, often under 100 ng/mL, with a low transferrin saturation. A high soluble transferrin receptor confirms that iron deficiency is present. Absent stainable iron on a bone marrow biopsy settles it if the stem offers one.

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