General MedicineNMC Grounded

Iron Deficiency Anemia: Iron Kinetics, Ferritin & Microcytic Anemias

Harrison's Principles of Internal Medicine 21st Ed · Ch 93 Iron Deficiency Anemia

Verified Clinical DiagramHarrison's Principles of Internal Medicine 21st Ed · Ch 93 Iron Deficiency Anemia

High-Yield Clinical Pearls & Exam Keys

Serum ferritin is the most sensitive and specific non-invasive laboratory marker of total body iron stores; a level < 15 ng/mL is 99% specific for iron deficiency.

Hepcidin, synthesized by the liver, binds to the basolateral iron exporter Ferroportin and induces its internalization and lysosomal degradation, blocking iron release into circulation.

The peripheral blood smear in iron deficiency displays microcytic, hypochromic red blood cells with marked anisopoikilocytosis and characteristic elongated 'pencil cells' (cigar cells).

Ask Dr. Medarro about General Medicine

Instant NMC-grounded answers with standard textbook citations

AI Senior Mentor

Or tap a high-yield exam question:

Sequential Laboratory Depletion in Iron Deficiency

Key #1

Stage 1 (Storage Depletion): Serum Ferritin falls (< 15-30 mcg/L); bone marrow Prussian blue iron stores disappear

Key #2

Stage 2 (Iron-Deficient Erythropoiesis): Serum Iron drops, TIBC rises, Transferrin Saturation drops (< 16%)

Key #3

Stage 3 (Frank Anemia): Hemoglobin drops with Microcytic Hypochromic indices (low MCV < 80 fL, low MCH) & elevated RDW

Differential Diagnosis of Microcytic Hypochromic Anemia

Laboratory Parameter	Iron Deficiency Anemia	Anemia of Chronic Disease
Serum Ferritin	Decreased (< 15 - 30 ng/mL; diagnostic gold standard)	Normal or Markedly Elevated (acute phase reactant)
Total Iron Binding Capacity (TIBC)	Elevated (> 360 mcg/dL)	Decreased or Normal (< 250 mcg/dL)
Red Cell Distribution Width (RDW)	Elevated (> 15%; high anisocytosis)	Normal or mildly elevated

Interactive Clinical Vignette Practice

Live Rule-Out Engine

Case Vignette #1NEET-PG Calibrated

A 62-year-old postmenopausal woman presents with progressive fatigue and exertional dyspnea. Complete blood count shows: Hb 8.2 g/dL, MCV 68 fL, MCH 21 pg, RDW 18.2%. Peripheral smear reveals microcytic hypochromic RBCs with prominent pencil cells. Serum ferritin is 8 ng/mL. She has no menorrhagia or visible hematochezia. What is the most critical next step in clinical management?

APrescribe oral ferrous ascorbate and follow up in 6 months

BPerform Upper GI endoscopy and full Colonoscopy to identify source of occult GI bleeding

CPerform urgent hemoglobin electrophoresis for beta-thalassemia

DAdminister intramuscular vitamin B12 injections weekly

Comprehensive Clinical & Pathophysiological Breakdown

**1. Dietary Forms & Intestinal Absorption** Total body iron in a healthy adult is approximately 3.5 to 4.5 g (70% in hemoglobin, 25% in ferritin/hemosiderin storage, and 5% in myoglobin/cytochromes). * **Site of Absorption**: Duodenum and upper proximal jejunum. * **Dietary Forms**: - *Heme Iron*: Derived from meat/hemoglobin; absorbed intact across enterocyte apical membranes via Heme Carrier Protein 1 (HCP1). - *Non-Heme Iron*: In ferric state (\( \text{Fe}^{3+} \)); must be reduced to ferrous state (\( \text{Fe}^{2+} \)) by apical **Duodenal Cytochrome B (DCYTB)** before uptake via the **Divalent Metal Transporter 1 (DMT1)**. * **Basolateral Export**: Ferrous iron is exported into circulation via **Ferroportin-1 (FPN1)** and reoxidized to ferric iron by the ferroxidase **Hephaestin** (enterocyte) or **Ceruloplasmin** (systemic) to enable binding to Transferrin. **2. Hepcidin: The Master Systemic Regulator** Hepcidin is a 25-amino acid peptide hormone synthesized by hepatocytes in response to iron overload and inflammation (IL-6 via STAT3 pathway): * **Mechanism**: Hepcidin binds to Ferroportin, inducing its internalization, ubiquitination, and lysosomal degradation. * **High Hepcidin** (Inflammation/Anemia of Chronic Disease): Blocks iron release from macrophages and enterocytes, causing low serum iron despite high marrow stores. * **Low Hepcidin** (Hypoxia/Iron deficiency/Ineffective erythropoiesis): Enhances Ferroportin expression, maximizing intestinal absorption and macrophage iron release. **3. 🔬 High-Yield Clinical Correlations** * **Iron Deficiency Anemia (IDA)**: - *Pathophysiology*: Negative iron balance causes sequential depletion: first absent bone marrow iron stores (low Ferritin <15 mcg/L), followed by increased Total Iron Binding Capacity (TIBC), decreased Transferrin saturation (<16%), and finally microcytic hypochromic red cell morphology. - *Clinical Signs*: Pallor, angular stomatitis, atrophic glossitis, and **Koilonychia** (spoon-shaped concave nails). - *Plummer-Vinson Syndrome*: Triad of Iron deficiency anemia, post-cricoid dysphagia (esophageal webs), and atrophic glossitis with increased risk of squamous cell carcinoma. **4. 📖 Standard Textbook Reference** * *Harper's Illustrated Biochemistry*, 32nd Ed., Ch. 50: Micronutrients (Minerals), pp. 582–590. * *Robbins and Cotran Pathologic Basis of Disease*, 10th Ed., Ch. 14: Red Blood Cell Disorders, pp. 638–644.

Viva Examiner Traps & Model Answers

Oral Exam Prep

What is the Mentzer index, and how does it differentiate Iron Deficiency from Thalassemia Trait?

Mentzer Index = MCV / RBC count (in millions/mcL). A ratio > 13 suggests Iron Deficiency Anemia (fewer, smaller red cells). A ratio < 13 strongly suggests Beta-Thalassemia Trait (many very small, uniform microcytic red cells with high RBC count > 5.0 million).

What is Koilonychia, and what is its pathophysiological significance?

Koilonychia ('spoon-shaped nails') is the upward curling of the lateral margins of the fingernails with central depression. It reflects impaired sulfur-containing protein cross-linking in the nail matrix due to long-standing tissue iron deficiency.

Why is oral iron therapy continued for 3 to 6 months AFTER hemoglobin normalizes?

Hemoglobin level normalizes within 6 to 8 weeks. Continued therapy for 3 to 6 months is necessary to fully replenish depleted reticuloendothelial iron stores in the bone marrow and liver (restoring ferritin levels).

Additional Exam Practice Vignettes (1)

Case Vignette #2

A 26-year-old pregnant woman is evaluated for mild anemia. Hemogram shows: Hb 10.4 g/dL, MCV 64 fL, RBC count 5.8 million/mcL. RDW is normal at 12.8%. Serum ferritin is 95 ng/mL. The Mentzer Index (MCV / RBC count) is calculated at 11.0. What is the most likely diagnosis?

A Mentzer index < 13, normal ferritin, normal RDW, and an elevated RBC count (>5.0 million) in the setting of microcytosis is classic for Beta-Thalassemia Trait.

Free Student Account Required

Unlock Complete Viva Traps & Additional Case Vignettes

Access model examiner answers, comprehensive rule-out breakdowns, and 4K spotter explanations.

Use email and password instead

Free student account•No credit card required

Medarro Study Hub

Want 50+ Clinical Vignettes & 4K 3D Spotters on General Medicine?

Practice Spaced Repetition Decathlon, generate instant 7-day adaptive study plans, and upload your college PDFs into the personal vault.

Related High-Yield Chapters

Surviving Sepsis Campaign Acute Coronary Syndrome Status Epilepticus Resuscitation