Iron Deficiency Anemia (IDA) — Examination Question Bank

Physiology of Iron Metabolism & Absorption

Question	Answer
1. Detail the physiology of dietary iron absorption in the human intestine.	Dietary iron exists in two forms: 1) Heme Iron ($10-15\%$ of diet, from meat/fish): Highly bioavailable ($20-30\%$ absorbed). Absorbed intact across the apical enterocyte membrane via the Heme Carrier Protein 1 (HCP-1); intracellular heme oxygenase-1 releases free ferrous iron ($ ext{Fe}^{2+}$). 2) Non-Heme Iron ($85-90\%$ of diet, from cereals, vegetables, dairy): Exists predominantly as insoluble ferric ($ ext{Fe}^{3+}$) iron. Low bioavailability ($2-10\%$). - Apical Reduction: The brush-border enzyme Duodenal Cytochrome B (Dcytb) reduces $ ext{Fe}^{3+}$ to absorbable ferrous $ ext{Fe}^{2+}$ (enhanced by gastric acid and ascorbic acid/Vitamin C). - Apical Entry: Transported into the enterocyte by the Divalent Metal Transporter 1 (DMT-1) (co-transported with $ ext{H}^+$). - Basolateral Export: Transported across the basolateral membrane into circulation by the iron exporter Ferroportin-1 (FPN-1). - Oxidation & Binding: The basolateral multicopper ferroxidase Hephaestin (and circulating Ceruloplasmin) re-oxidizes $ ext{Fe}^{2+}$ back to $ ext{Fe}^{3+}$, allowing high-affinity binding to plasma Transferrin for delivery to the bone marrow.
2. What is Hepcidin and how does it regulate systemic iron homeostasis?	Hepcidin is a 25-amino acid peptide hormone synthesized exclusively by hepatocytes; it is the master negative regulator of systemic iron availability. - Mechanism of Action: Hepcidin binds directly to the basolateral iron exporter Ferroportin, inducing its internalization, ubiquitination, and lysosomal degradation. - Physiological Consequences: - High Hepcidin (in systemic inflammation, infection, IL-6 elevation): Traps iron inside duodenal enterocytes and splenic/hepatic macrophages $
ightarrow$ produces hypoferremia and Anemia of Chronic Disease. - Low Hepcidin (in Iron Deficiency Anemia, hypoxia, or expanded ineffective erythropoiesis via erythroferrone): Increases cell-surface ferroportin expression $
ightarrow$ maximizes intestinal iron absorption and macrophage iron release into circulation.
3. Trace the progressive stages of Iron Deficiency.	Iron deficiency evolves through three distinct pathophysiological phases: 1) Stage 1: Iron Depletion (Storage Iron Exhaustion): - Bone marrow storage iron is depleted; Serum Ferritin drops $<12-15 ext{ mcg/L}$. - Serum iron, TIBC, transferrin saturation, hemoglobin, and red cell indices remain completely NORMAL. 2) Stage 2: Iron-Deficient Erythropoiesis (Transport Iron Deficit): - Storage iron is exhausted; circulating transport iron falls. - Serum Iron decreases ($<40 ext{ mcg/dL}$), TIBC rises ($>400 ext{ mcg/dL}$), and Transferrin Saturation falls $<16\%$. - Free Erythrocyte Protoporphyrin (FEP) and Soluble Transferrin Receptor (sTfR) rise. - Hemoglobin is still within normal limits, but reticulocyte hemoglobin content (CHr) begins to drop. 3) Stage 3: Frank Iron Deficiency Anemia (Functional Iron Deficit): - Inadequate iron supply to developing erythroblasts compromises hemoglobin synthesis. - Hemoglobin and Hematocrit drop below age-specific cutoffs. - Progressive microcytosis and hypochromia develop: MCV $<70 ext{ fL}$, MCH $<24 ext{ pg}$, MCHC $<31 ext{ g/dL}$, and RDW $>15-18\%$.

Diagnostic Differentiation of Microcytic Anemias

Question	Answer
4. How do you differentiate Iron Deficiency Anemia from Beta-Thalassemia Trait (Minor) on CBC and Smear?
5. Detail the common Mathematical Discriminant Indices for Microcytic Anemia.	1) Mentzer Index: $$ ext{Mentzer Index} = rac{ ext{MCV (fL)}}{ ext{RBC Count (millions/}\mu ext{L})}$$ - $>13$: Favors Iron Deficiency Anemia (Sensitivity $pprox 85\%$, Specificity $pprox 85\%$). - $<13$: Favors Beta-Thalassemia Trait. 2) Green-King Index: $$ ext{Green-King Index} = rac{ ext{MCV}^2 imes ext{RDW}}{ ext{Hb (g/dL)} imes 100}$$ - $>72$: Iron Deficiency Anemia. - $<72$: Thalassemia Trait. 3) Shine & Lal Index: $$ ext{Shine & Lal Index} = rac{ ext{MCV}^2 imes ext{MCH}}{100}$$ - $>1530$: Iron Deficiency Anemia. - $<1530$: Thalassemia Trait.
6. How do you differentiate Iron Deficiency Anemia from Anemia of Chronic Disease (ACD)?

Pharmacotherapy, Protocols & Monitoring

Question	Answer
7. Formulate the therapeutic prescription for Oral Iron Therapy in a child.	- Recommended Therapeutic Dosage: $3 ext{ to }6 ext{ mg/kg/day}$ of ELEMENTAL IRON administered orally in 2 to 3 divided doses. - Preferred Formulations: - Ferrous Ascorbate / Ferrous Bisglycinate: Preferred due to superior gastrointestinal tolerance and uninhibited absorption. - Ferrous Sulfate ($20\%$ elemental iron): Standard low-cost public health formulation (e.g., $150 ext{ mg}$ tablet contains $30 ext{ mg}$ elemental iron). - Ferrous Fumarate ($33\%$ elemental iron). - Administration Rules: - Give on an empty stomach (1 hour before or 2 hours after meals) or with citrus fruit juice / Vitamin C. - Strictly avoid co-administration with cow's milk, dairy products, tea, cereals (phytates), or calcium syrups, which chelate and precipitate iron. - Counsel parents that stools will turn harmlessly dark black/greenish; mild transient constipation or loose stools may occur.
8. Detail the chronological timeline of hematological response to oral iron.	Following oral iron administration, response unfolds in a precise temporal sequence: 1) 12 to 24 Hours: Rapid symptomatic improvement; child becomes less irritable, more alert, and appetite returns (due to rapid replenishment of intracellular iron-containing enzymes: cytochrome c, cytochrome oxidase, and monoamine oxidase). 2) 36 to 48 Hours: Erythroid hyperplasia in bone marrow. 3) 5 to 7 Days: Reticulocyte Crisis (Peak Reticulocytosis, typically $5-15\%$)—the earliest objective, confirmatory proof of therapeutic response! 4) 3 to 4 Weeks: Hemoglobin rises steadily at a rate of $0.7 ext{ to }1.0 ext{ g/dL per week}$ (minimum rise of $>1.0-2.0 ext{ g/dL}$ by Day 28). 5) 6 to 8 Weeks: Normalization of Hemoglobin and red cell indices. 6) 2 to 3 Months: VIVA TRAP: Iron therapy must NOT be halted when hemoglobin reaches normal levels! Continue for an additional 2 to 3 months after Hb normalization to fully replenish bone marrow and liver storage iron pools (Serum Ferritin).
9. What are the Indications for Parenteral (Intravenous) Iron Therapy and how is the dose calculated?	- Indications for IV Iron in Pediatrics: 1) Severe intractable gastrointestinal intolerance or severe vomiting from oral iron. 2) Proven intestinal malabsorption syndromes (uncontrolled celiac disease, extensive Crohn disease, short bowel syndrome). 3) Continuous, ongoing chronic blood loss exceeding the rate of oral intestinal absorption (e.g., severe hereditary hemorrhagic telangiectasia, active inflammatory bowel disease). 4) Non-compliance with oral therapy despite intensive counseling. 5) Severe anemia in chronic kidney disease (CKD) on erythropoietin therapy. - Parenteral Iron Formulations: Iron Sucrose ($100 ext{ mg/vial}$) or Ferric Carboxymaltose (FCM) ($500 ext{ mg/vial}$—can be given as a single high-dose infusion over 15 minutes). - Dose Calculation (Ganzoni Formula): $$ ext{Total Iron Deficit (mg)} = ext{Weight (kg)} imes ( ext{Target Hb} - ext{Actual Hb in g/dL}) imes 2.4 + ext{Iron Depots (mg)}$$ (Where factor 2.4 accounts for blood volume $pprox 80 ext{ mL/kg}$ and iron content of $ ext{Hb} pprox 0.34\%$; Iron Depots = $10-15 ext{ mg/kg}$ up to max $500 ext{ mg}$).
10. VIVA TRAP: What is your diagnostic approach to a child who fails to respond to oral iron after 4 weeks?	If hemoglobin fails to rise by at least $1.0 ext{ g/dL}$ after 4 weeks of compliant therapy, evaluate the 5 C's of Refractory Iron Deficiency Anemia: 1) Compliance (Most Common!): Confirm whether the child actually swallowed the medication; check if stools turned dark black (absence of dark stools indicates non-adherence or spitting out syrup). 2) Correct Dosing & Administration: Verify that the dose was calculated based on elemental iron ($3-6 ext{ mg/kg}$), not gross salt weight, and that it was not administered simultaneously with milk or tea. 3) Continued Unrecognized Blood Loss: Active occult gastrointestinal bleeding: Meckel diverticulum (technetium pertechnetate scan), juvenile polyps, chronic cow's milk protein enteropathy, hookworm infestation. 4) Co-existing Malabsorption / Dual Deficiency: Subclinical Celiac Disease (perform anti-tTG IgA), Helicobacter pylori gastritis, concurrent Vitamin B12 / Folate deficiency (dimorphic anemia), or co-existing systemic infection/inflammation suppressing marrow response. 5) Co-existing Hemoglobinopathy / Rare Genetic Channelopathy: Re-evaluate initial diagnosis: Beta-Thalassemia Trait (Hb will not rise with iron), or rare Iron-Refractory Iron Deficiency Anemia (IRIDA) caused by autosomal recessive loss-of-function mutations in TMPRSS6 (matriptase-2), causing inappropriately elevated hepcidin that permanently blocks intestinal ferroportin!