How should I interpret and manage a 9-year-old child with a mean platelet volume of 9 fL, total iron‑binding capacity of 450 µg/dL, and transferrin saturation of 20%?

Iron Deficiency Anemia with Reactive Thrombocytosis

This 9-year-old has iron deficiency anemia (IDA) based on elevated TIBC (450 µg/dL) and low transferrin saturation (20%), and should be started immediately on oral iron supplementation at 3–6 mg/kg/day of elemental iron while investigating the source of iron loss. 1

Laboratory Interpretation

Iron Studies Confirm Iron Deficiency

• TIBC of 450 µg/dL is elevated, indicating depleted iron stores—TIBC rises as a compensatory mechanism to mobilize all available tissue iron before serum iron falls. 1, 2
• Transferrin saturation of 20% is low (normal >20–25%), confirming insufficient iron availability for erythropoiesis. 1
• TIBC or transferrin measurement alone outperforms iron and saturation indices in predicting iron deficiency, with area under ROC curve of 0.94 versus 0.77 for iron alone. 3
• During early iron deficiency, TIBC elevation occurs before serum iron decreases, representing a compensatory mechanism to maintain normal erythropoiesis. 2

Mean Platelet Volume is Normal

• MPV of 9 fL is within normal range for a 9-year-old child (normal pediatric range 7.4–10.4 fL). 4
• Normal MPV does not exclude iron deficiency—MPV has no diagnostic value in pediatric conditions and should not influence clinical decision-making. 4

Likely Reactive Thrombocytosis (Not Thrombocytopenia)

• Although platelet count was not provided in your question, iron deficiency is a common cause of reactive thrombocytosis in children, occurring in 3–13% of hospitalized children. 5, 6
• Reactive thrombocytosis from iron deficiency is 60 times more common than primary thrombocytosis in children and requires no specific treatment beyond addressing the underlying iron deficiency. 5, 6

Immediate Management Algorithm

Step 1: Initiate Iron Supplementation

• Start oral elemental iron 3–6 mg/kg/day divided in 2–3 doses immediately. 5
• Continue treatment for 3–6 months to replenish iron stores, even after hemoglobin normalizes. 1

Step 2: Investigate Source of Iron Loss

• Dietary history: Assess for inadequate dietary iron intake (excessive milk consumption, vegetarian diet, picky eating). 1
• Gastrointestinal blood loss: Screen for occult blood in stool if dietary insufficiency does not explain the deficiency. 1, 5
• Malabsorption: Consider celiac disease screening if poor response to oral iron or additional symptoms present. 1

Step 3: Follow-Up Laboratory Monitoring

• Repeat CBC in 4–6 weeks to confirm response to iron therapy—expect hemoglobin rise of 1–2 g/dL and normalization of iron studies. 5
• If platelet count is elevated, it should normalize as iron stores are replenished. 5, 6

Critical Diagnostic Pitfalls to Avoid

• Do not delay iron supplementation while waiting for additional testing—iron deficiency is confirmed by elevated TIBC and low saturation, and treatment should begin immediately. 1, 3
• Do not attribute elevated platelets (if present) to a primary hematologic disorder without first treating iron deficiency, as reactive thrombocytosis resolves with iron repletion. 5, 6
• Do not order bone marrow examination—it is unnecessary when iron studies clearly demonstrate iron deficiency. 1
• Do not restrict activity or treat thrombocytosis (if present) with antiplatelet agents, as reactive thrombocytosis in children causes no thrombotic or hemorrhagic complications. 7, 6

When to Refer to Hematology

• Persistent thrombocytosis after 3 months of iron repletion warrants hematology consultation to exclude primary thrombocytosis. 6
• Lack of hemoglobin response after 4–6 weeks of adequate iron therapy suggests alternative diagnosis or malabsorption. 5
• Platelet count >1,000/μL (extreme thrombocytosis) requires hematology evaluation even if iron deficiency is present. 6