Internal MedicineHematologyIron‑Deficiency Anemia

Iron‑Deficiency Anemia

Must-Not-Miss / Red Flags

  • Hemodynamic instability: Hb <7 g/dL → risk of heart failure
  • Melena/hematochezia: undiagnosed GI malignancy
  • Plummer‑Vinson syndrome: dysphagia + IDA → risk of squamous cell carcinoma of esophagus
Patient Explanation
“Your body doesn’t have enough iron to make healthy red blood cells. We’ll give you iron supplements and find the cause of the low iron.”
Board Fact
“The most common cause of IDA in premenopausal women is menorrhagia; in postmenopausal women and men, it is GI bleeding until proven otherwise.”
ICD-10
D50.9

Definition & Core Concept

Iron‑deficiency anemia (IDA) is the most common form of anemia worldwide, caused by inadequate iron stores leading to impaired hemoglobin synthesis and microcytic, hypochromic red blood cells.

Epidemiology & Risk Factors

  • Affects 25% of the global population (WHO)
  • Most common in children under 5 years and premenopausal women
  • In developing countries, hookworm infection is a major cause

Pathophysiology (Rule of 3)

  1. Inadequate iron intake/absorption or chronic blood loss → depletion of iron stores
  2. Ferritin levels drop → decreased iron supply to bone marrow
  3. Impaired heme synthesis → microcytic, hypochromic anemia → reduced oxygen‑carrying capacity

Clinical Presentation

  • Fatigue, weakness, dyspnea on exertion, palpitations
  • Pallor, brittle nails, hair loss
  • Pica (craving for ice, dirt, or starch)
  • Restless legs syndrome

Diagnostic Workup

CBC: microcytic anemia (MCV <80 fL), increased RDW. Serum ferritin: <15 ng/mL (diagnostic). Serum iron: low; TIBC: increased; transferrin saturation: <15%. Peripheral smear: hypochromic microcytes, pencil cells.

Management Protocol

  1. Oral iron: Ferrous sulfate 325 mg (65 mg elemental iron) TID; expect Hb rise of 1 g/dL per week
  2. IV iron: for malabsorption (celiac, gastric bypass), severe anemia, or intolerance to oral iron
  3. Blood transfusion: if Hb <7 g/dL or hemodynamic instability
  4. Treat underlying cause: GI workup (endoscopy/colonoscopy) in all postmenopausal women and men

Complications & Prognosis

  • High‑output heart failure in severe anemia
  • Impaired cognitive and motor development in children
  • Increased susceptibility to infections

ICU Criteria

ICU admission rarely necessary unless severe anemia (Hb <5 g/dL) with cardiovascular collapse.

Clinical Vignette

A 32‑year‑old woman presents with fatigue and dyspnea on exertion for 2 months. She reports heavy menstrual periods. Hb is 8.2 g/dL, MCV 72 fL, ferritin 8 ng/mL. Peripheral smear shows microcytic hypochromic cells.

Pearls & Pitfalls

  • A normal ferritin does not rule out IDA if inflammation is present (ferritin is an acute‑phase reactant).
  • In mixed anemia (e.g., B12 + iron deficiency), MCV may appear normal – always check RDW and peripheral smear.

Discharge & Follow-Up

Recheck Hb in 2‑4 weeks to confirm response. Continue iron for 3‑6 months to replenish stores. Refer for gynecologic or GI evaluation based on suspected source of blood loss.

Literature & Guidelines

BSG Guidelines for the management of iron deficiency anemia. PMID: 32358087.

Personal Clinical Notes