Iron Deficiency Anemia
Hematology
Illness script · Hematology
Iron Deficiency Anemia
Most common anemia worldwide; caused by depleted iron stores leading to impaired hemoglobin synthesis and microcytic, hypochromic RBCs.
This illness script for Iron Deficiency Anemia covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- Most common cause: chronic blood loss (GI in men/postmenopausal women; menstrual in premenopausal women)
- Infants fed cow's milk exclusively; toddlers with low dietary iron
- Pregnancy increases iron demand significantly
- Malabsorption: celiac disease, post-gastrectomy, H. pylori infection
- Vegetarian/vegan diet with low bioavailable iron
02
Presentation
- Fatigue, pallor, exertional dyspnea — often insidious onset
- Pica (craving ice = pagophagia, dirt, clay) — highly specific symptom
- Koilonychia (spoon-shaped nails), angular cheilitis, glossitis
- Plummer-Vinson syndrome: dysphagia + iron deficiency anemia + esophageal web
- Restless leg syndrome association
- Tachycardia, conjunctival pallor on exam
03
Pathophysiology
- Depleted iron stores → reduced transferrin saturation → inadequate heme synthesis
- Insufficient hemoglobin → small, pale (microcytic, hypochromic) RBCs
- Compensatory increase in transferrin (TIBC) and decrease in serum ferritin
- Erythropoiesis becomes iron-restricted; reticulocyte count inappropriately low
04
Diagnostics
- CBC: low MCV (<80 fL), low MCH; RDW elevated (anisocytosis)
- Low serum ferritin (<12 ng/mL) — most sensitive/specific single test for iron deficiency
- Low serum iron, high TIBC, low transferrin saturation (<16%)
- Peripheral smear: microcytic hypochromic cells, pencil cells, target cells
- Gold standard: bone marrow biopsy (absent iron staining) — rarely needed clinically
- Always investigate source: colonoscopy/EGD in men and postmenopausal women
05
Management
- Oral ferrous sulfate 325 mg TID on empty stomach — first-line
- Add vitamin C to enhance absorption; avoid calcium/antacids concurrently
- Expect reticulocyte peak at 7–10 days; Hgb normalizes in ~2 months
- Continue oral iron 3–6 months after Hgb normalizes to replete stores
- IV iron (ferric gluconate, ferumoxytol) if malabsorption, intolerance, or severe deficiency
- Transfuse pRBCs only if hemodynamically unstable or severely symptomatic
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Anemia of Chronic Disease
ACD: low TIBC, normal/high ferritin, low serum iron — ferritin is key differentiator
Thalassemia Trait
Thalassemia: normal/high RBC count, normal ferritin, elevated HbA2 on electrophoresis; Mentzer index <13
Sideroblastic Anemia
Sideroblastic: high serum iron, high ferritin, ringed sideroblasts on marrow biopsy
Lead Poisoning
Lead poisoning: basophilic stippling on smear, elevated blood lead level, exposure history
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Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.