A 10-month-old infant on cow's milk formula (unmodified) and no solid foods presents with pallor and irritability. CBC shows Hb 7.1 g/dL, MCV 62 fL, MCH 19 pg, serum ferritin 4 ng/mL, serum iron 28 μg/dL. Serum lead level is normal. What is the PRINCIPAL mechanism by which unmodified cow's milk causes iron deficiency anemia in infants?

• A Cow's milk has no iron content and exclusively provides calcium which blocks iron absorption
• B Cow's milk causes an IgE-mediated allergic reaction that prevents intestinal absorption of all micronutrients
• C High phosphate content in cow's milk chelates iron in the gastrointestinal lumen making it insoluble
• D Cow's milk proteins cause microscopic gastrointestinal blood loss, and the low iron content with low bioavailability of cow's milk iron compounds the deficiency ✓

Explanation

Unmodified cow's milk causes iron deficiency anemia in infants through two mechanisms: (1) cow's milk proteins (especially heat-labile proteins) cause microscopic gastrointestinal blood loss by inducing a non-IgE-mediated cow's milk protein enteropathy; and (2) cow's milk is naturally low in iron (~0.5 mg/L) with poor bioavailability. Together, ongoing occult GI blood loss plus inadequate iron intake causes negative iron balance. The mechanism is NOT primarily IgE-mediated allergy. While calcium does compete with iron absorption, the GI blood loss mechanism is more significant for cow's milk-specific iron deficiency anemia.

Reference: Ghai Essential Pediatrics, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.