Iron Deficiency Anemia (IDA)

An article by Dr. Kasturi Mandal | Last updated: June 2025

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1. Definition & Epidemiology

• IDA is the most common form of anemia globally, accounting for approximately 50–60% of all anemia cases.
• Globally, moderate IDA affects roughly 610 million people (~8.8% of the population), with pregnant women affected in up to 52% of cases.
• In the US, about 10–11% of women of reproductive age, 2% of adult men, and up to 15% of children aged 1–3 are affected.

2. Pathophysiology & Causes

Iron is essential for hemoglobin synthesis. Depletion of iron stores may result from inadequate intake, impaired absorption, increased demand, or chronic loss.

Stages of iron deficiency:

• Pre-latent: low iron stores, normal serum iron
• Latent: falling serum iron and transferrin saturation, low ferritin
• Overt IDA: anemia with low hemoglobin, depleted stores

Common causes include: heavy menstrual bleeding, occult GI blood loss (e.g., ulcers, colon cancer), hookworm infection (in endemic areas), malabsorption disorders (e.g., coeliac disease, post-gastrectomy), pregnancy and growth spurts.

3. Risk Factors

High-risk groups include women of childbearing age (especially menstruating or pregnant), infants and young children, vegetarians/vegans, adolescents, older adults, and individuals with low socioeconomic status or chronic diseases (e.g., IBD, kidney disease).

4. Clinical Features

Symptoms often begin insidiously: fatigue, weakness, pallor, dyspnea on exertion, tachycardia, headache, cold extremities, and pica (e.g. ice or dirt). Subtle signs may include brittle hair, irritability, depression, and decreased concentration even before traditional anemia symptoms emerge.

Signs on physical exam: pallor (skin/conjunctiva), tachycardia, koilonychia, glossitis, and in severe cases signs of heart failure.

5. Diagnosis & Laboratory Evaluation

CBC: low hemoglobin/hematocrit, microcytic (MCV < 80 fL), hypochromic (low MCH/MCHC), elevated RDW due to variation in RBC size. Iron studies:

• ↓ Serum ferritin (most specific; <15 ng/mL in adults suggests iron deficiency; <10 ng/mL indicates clear IDA)
• ↓ Serum iron, ↑ Total iron-binding capacity (TIBC), ↓ transferrin saturation (<16 %)

Additional lab markers include elevated red cell zinc protoporphyrin or low reticulocyte hemoglobin content. In men and post-menopausal women, evaluation for GI blood loss (endoscopy, colonoscopy) is essential. Test for coeliac disease and Helicobacter pylori in malabsorption contexts.

6. Treatment & Management

Oral iron supplementation (first-line): usually ferrous sulfate/fumarate/gluconate, 100–200 mg elemental iron daily or every other day for better absorption/tolerability. Continue therapy for at least 3 months after hemoglobin normalization to replenish stores. Common side effects: GI distress (constipation, nausea, dark stools) leading to poor adherence.

Intravenous iron (second-line or earlier when indicated): used when oral iron fails or is poorly tolerated, in malabsorptive conditions, severe anemia, ongoing bleeding, or pregnancy needing rapid correction. Modern IV formulations raise hemoglobin faster and with fewer GI effects. Reassess hemoglobin at ~2 weeks; if Hb rise <1 g/dL by day 14, reconsider therapy.

7. Prognosis & Complications

With appropriate treatment, prognosis is excellent. If underlying cause is not addressed, anemia may recur. Chronic untreated IDA can contribute to heart complications (tachycardia, heart failure), impaired immunity, developmental delays in children, and pregnancy risks. Emerging data link unexplained IDA to occult colorectal cancer, underscoring the need for thorough evaluation.

Summary of Key Features

🧠 Final Takeaway

Iron deficiency anemia is a treatable yet common global disorder whose root causes vary across individuals and regions. Early detection via laboratory evaluation and prompt treatment—usually through iron supplementation and dietary adjustment—can lead to swift improvement. Always seek medical advice to evaluate symptoms and guide treatment safely.