Diagnosis: Iron Deficiency Anemia with Reactive Thrombocytosis
The most likely diagnosis for this 5-year-old male with hemoglobin 101 g/L (10.1 g/dL) and platelet count of 824 × 10⁹/L is iron deficiency anemia with reactive thrombocytosis. This combination of mild anemia and marked thrombocytosis in a young child is characteristic of iron deficiency, which is the most common cause of reactive thrombocytosis in pediatric populations 1, 2.
Key Diagnostic Features
Iron deficiency anemia commonly presents with reactive thrombocytosis, with platelet counts frequently exceeding 400-600 × 10⁹/L and occasionally reaching extreme levels above 1000 × 10⁹/L 1, 2. The platelet count of 824 × 10⁹/L falls well within this expected range for iron deficiency-associated thrombocytosis.
Clinical Context Supporting Iron Deficiency
- Age-appropriate presentation: Five-year-old children are at high risk for iron deficiency due to dietary insufficiency, rapid growth, or chronic blood loss 1
- Mild anemia: The hemoglobin of 101 g/L represents mild anemia consistent with iron deficiency rather than severe hematologic disease 1
- Preserved white blood cell production: Unlike aplastic anemia or leukemia, iron deficiency maintains normal leukocyte counts 3
Alternative Diagnoses to Exclude
Kawasaki Disease (Less Likely)
While Kawasaki disease can present with thrombocytosis in the subacute phase, it requires fever persisting at least 5 days plus 4 of 5 principal clinical features (extremity changes, polymorphous exanthema, conjunctival injection, oral/lip changes, cervical lymphadenopathy) 4. Thrombocytosis in Kawasaki disease typically occurs during the subacute phase (days 7-14) rather than at initial presentation 4. Without fever and characteristic mucocutaneous findings, this diagnosis is unlikely.
Sickle Cell Disease with Splenic Sequestration (Excluded)
Splenic sequestration in sickle cell disease presents with rapidly enlarging spleen, hemoglobin decrease >2 g/dL below baseline, and mild to moderate thrombocytopenia, not thrombocytosis 4. The presence of marked thrombocytosis effectively excludes this diagnosis.
Wiskott-Aldrich Syndrome (Excluded)
WAS presents with thrombocytopenia and characteristically small platelets (3.8-5.0 fL versus normal 7.1-10.5 fL) 4. The presence of thrombocytosis rather than thrombocytopenia completely excludes this X-linked disorder 4.
Myeloproliferative Neoplasms (Unlikely in This Age)
While refractory anemia with ring sideroblasts associated with thrombocytosis (RARS-T) can present with anemia and platelet counts of 515-1,100 × 10⁹/L, approximately 60% carry JAK2 V617F mutations 5, 6. However, this is a disease of adults, not 5-year-old children, making it extremely unlikely 5, 6.
Diagnostic Workup Required
Essential Initial Testing
- Complete blood count with differential and peripheral blood smear: Confirm microcytic hypochromic anemia and true thrombocytosis; evaluate for abnormal cells 3
- Iron studies: Serum ferritin, transferrin saturation, and serum iron to confirm iron deficiency 4, 1
- Reticulocyte count: Should be normal or mildly elevated in iron deficiency, distinguishing it from aplastic anemia 3
Additional Evaluation
- Mean corpuscular volume (MCV): Expected to be low in iron deficiency anemia 4, 1
- Red cell distribution width (RDW): Typically elevated in iron deficiency 1
- Stool occult blood testing: To identify gastrointestinal blood loss as a potential cause 4
Clinical Significance and Management Implications
Reactive thrombocytosis in iron deficiency anemia, even when extreme, does not typically require cytoreductive therapy 2. The thrombocytosis resolves with iron supplementation and correction of the underlying anemia 1, 2.
Important Caveats
Cerebral venous thrombosis risk: Although rare, the combination of iron deficiency anemia and reactive thrombocytosis has been associated with thrombotic complications, including cerebral venous thrombosis in children 7. Monitor for neurological symptoms such as headache, vomiting, mental status changes, or seizures.
Plasma viscosity: Despite marked thrombocytosis, plasma viscosity is not significantly elevated in reactive thrombocytosis compared to thrombocythemia, as these are non-clonal platelets 1
Treatment response: Platelet counts normalize within weeks to months of iron supplementation, confirming the reactive nature of the thrombocytosis 2
The diagnosis should be confirmed with iron studies showing low serum ferritin and low transferrin saturation, followed by oral iron supplementation as definitive treatment 4, 2.