What is the likely diagnosis and recommended management for an 11‑month‑old infant with hemoglobin 11.9 g/dL, hematocrit 34.9 %, mean corpuscular volume 70.8 fL (microcytosis), and platelet count 510 ×10⁹/L?

Likely Diagnosis: Iron Deficiency Anemia with Reactive Thrombocytosis

This 11-month-old infant has iron deficiency anemia, confirmed by microcytosis (MCV 70.8 fL), mild anemia (Hb 11.9 g/dL), and reactive thrombocytosis (platelets 510 × 10⁹/L). The combination of these findings is pathognomonic for iron deficiency in this age group. 1

Diagnostic Reasoning

Why This Is Iron Deficiency Anemia

• Microcytosis is the earliest laboratory sign of iron deficiency, appearing even before hemoglobin falls below the anemia threshold; an MCV of 70.8 fL in an 11-month-old (normal range 80–100 fL) confirms iron-deficient erythropoiesis. 1

• Thrombocytosis peaks in the third week of iron deficiency and serves as a reactive marker; platelet elevation to 510 × 10⁹/L strongly favors iron deficiency over anemia of chronic disease, where platelet elevation is uncommon. 1

• The hemoglobin of 11.9 g/dL represents mild anemia (WHO threshold <11 g/dL for children 6–59 months), but the severity of microcytosis relative to the degree of anemia is characteristic of iron deficiency rather than thalassemia trait. 2, 3

Differential Diagnosis Excluded

• Thalassemia trait is unlikely because iron deficiency typically shows more severe microcytosis relative to the hemoglobin level, and thalassemia would present with a normal or elevated red blood cell count despite microcytosis. 1, 4

• Anemia of chronic disease is excluded by the presence of marked thrombocytosis and the absence of inflammatory symptoms in a well-appearing infant. 1

Immediate Diagnostic Confirmation

Essential Laboratory Tests

• Order serum ferritin immediately; a level <30 µg/L confirms depleted iron stores, while a cut-off of 45 µg/L provides optimal sensitivity and specificity in clinical practice. 1

• Measure transferrin saturation (TSAT); a value <16–20% confirms iron deficiency even if ferritin appears borderline. 1

• Check C-reactive protein (CRP) to rule out inflammation that could falsely elevate ferritin; in the absence of inflammation, ferritin <30 µg/L is diagnostic. 1

• A therapeutic trial of oral iron is an alternative definitive test when doubt remains; a hemoglobin rise ≥10 g/L within 2 weeks confirms iron deficiency even when initial iron studies are equivocal. 1, 4

Management Protocol

First-Line Treatment

• Begin oral iron supplementation with ferrous sulfate 3–6 mg/kg/day of elemental iron (typically ferrous sulfate 200 mg contains 65 mg elemental iron) given once daily or divided into 2–3 doses for at least three months after correction of anemia to replenish iron stores. 1

• Ascorbic acid (vitamin C) can be added to enhance iron absorption if tolerated. 1

• Alternative formulations include ferrous gluconate or ferrous fumarate if ferrous sulfate causes gastrointestinal side effects. 1

Expected Response and Monitoring

• Hemoglobin should rise ≥10 g/L within 2 weeks if iron deficiency is the cause; this rapid response confirms the diagnosis. 1

• Monitor hemoglobin and red cell indices at 4 weeks, then at three-monthly intervals for one year to ensure sustained response. 1

• Continue iron supplementation for at least 3 months after hemoglobin normalizes to replenish iron stores and prevent recurrence; target ferritin >50 µg/L. 1

Investigation of Underlying Cause

• Assess dietary history in detail: exclusive breastfeeding beyond 6 months without adequate iron-fortified complementary foods, exclusive formula feeding without iron fortification, or inadequate solid food intake (fewer than 3 meals per day with heme iron sources) are the primary risk factors. 5

• Evaluate for cow's milk protein intolerance if the infant consumes large volumes of cow's milk (>24 oz/day), which can cause occult gastrointestinal blood loss. 2

• Screen for celiac disease if there is failure to thrive, chronic diarrhea, or family history, as it accounts for 2–3% of iron deficiency cases. 1

Critical Pitfalls to Avoid

• Do not assume normal hemoglobin at 12 months protects against iron deficiency in the second year of life; 9.3% of infants who were non-anemic at 1 year develop iron deficiency anemia by 24 months, supporting the need to continue iron supplementation into the second year. 6, 7

• Do not delay treatment while awaiting ferritin results in a symptomatic infant with clear microcytosis and thrombocytosis; begin empiric iron therapy immediately, as the therapeutic response itself confirms the diagnosis. 1

• Do not order hemoglobin electrophoresis at this stage; it is indicated only when iron studies are normal or borderline, or when the MCV is disproportionately low relative to anemia severity after iron repletion. 1

• Do not attribute microcytosis to ethnic background without laboratory confirmation; thalassemia trait must be confirmed by testing, not presumed based on ethnicity alone. 4

• Do not stop iron supplementation once hemoglobin normalizes; continue for at least 3 months to replenish iron stores and prevent recurrence. 1

Prognosis and Long-Term Considerations

• Iron deficiency anemia in infancy is associated with long-term psychomotor, behavioral, and developmental effects, underscoring the importance of prompt diagnosis and adequate treatment. 7

• Adequate heme iron supplementation in 3 meals of solid food is essential for prevention of iron deficiency in one-year-old infants; dietary counseling should emphasize iron-fortified cereals, pureed meats, and iron-rich vegetables. 5