How should I evaluate and manage a 14-year-old girl with thrombocytosis (platelet count 830 × 10⁹/L) and no anemia?

Evaluation and Management of Thrombocytosis in a 14-Year-Old Female

This 14-year-old girl with a platelet count of 830 × 10⁹/L and no anemia most likely has reactive (secondary) thrombocytosis, which requires identification and treatment of the underlying cause but no antiplatelet therapy or cytoreduction.

Initial Diagnostic Approach

Confirm True Thrombocytosis

• Verify the elevated platelet count by repeating the complete blood count and reviewing a peripheral blood smear to exclude platelet clumping artifacts that can falsely elevate automated counts 1
• Have a hematopathologist examine the smear for platelet size (giant platelets suggest inherited disorders), red-cell morphology (schistocytes indicate thrombotic microangiopathy), and white-cell abnormalities (immature cells raise concern for myeloproliferative disease) 1

Distinguish Reactive from Primary Thrombocytosis

Reactive thrombocytosis is overwhelmingly more common in adolescents, occurring in 3–13% of hospitalized children, whereas primary (essential) thrombocythemia has an incidence of only 1 per million children—60 times lower than in adults 2. The median age at diagnosis of essential thrombocythemia is approximately 11 years, and platelet counts typically exceed 1,000 × 10⁹/L 2.

Key clinical features favoring reactive thrombocytosis:

• Platelet count 500–900 × 10⁹/L (this patient's count of 830 falls in the "moderate" range) 2
• Recent or concurrent infection, inflammation, or tissue injury 2, 3
• Normal hemoglobin and white blood cell count on CBC 1
• Absence of splenomegaly, hepatomegaly, or lymphadenopathy on physical examination 1

Red flags suggesting primary thrombocythemia or other hematologic malignancy:

• Platelet count persistently > 1,000 × 10⁹/L 2, 4
• Presence of organomegaly or lymphadenopathy 1, 5
• Additional cytopenias (anemia, leukopenia) or abnormal white-cell morphology on smear 1, 5
• Systemic symptoms: unexplained fever, weight loss, night sweats, or bone pain 1, 5

Targeted Etiologic Work-Up for Reactive Thrombocytosis

Most Common Causes in Adolescents

Infection accounts for approximately 30–75% of reactive thrombocytosis in children 2, 3. Osteomyelitis and septic arthritis produce higher platelet counts than other infections 3. Obtain a detailed history of recent viral respiratory illness, gastroenteritis, or bacterial infections 5, 3.

Iron deficiency is a frequent and reversible cause in adolescent females due to menstrual blood loss 5, 2. Although reactive thrombocytosis from iron deficiency typically produces platelet counts < 700 × 10⁹/L, extreme elevations (> 1,000 × 10⁹/L) have been documented, particularly with severe iron deficiency from celiac disease or malabsorption 6, 4.

Chronic inflammation (inflammatory bowel disease, connective tissue disorders) becomes more common after age 5 years 3.

Essential Laboratory Tests

• Iron studies (serum ferritin, iron, total iron-binding capacity): Iron deficiency is the most common treatable cause in menstruating adolescent girls 5, 2
• Inflammatory markers (ESR, CRP): Elevated in infection, tissue damage, or chronic inflammatory conditions 5
• Peripheral blood smear review by hematopathologist: Mandatory to exclude pseudothrombocytosis, identify giant platelets (inherited thrombocytopenias), schistocytes (thrombotic microangiopathy), or immature white cells (leukemia, myelodysplastic syndrome) 1, 5

When Bone Marrow Examination Is Required

Bone marrow aspiration and biopsy with flow cytometry and cytogenetics are mandatory if any of the following are present 1, 5:

• Platelet count > 600 × 10⁹/L persisting beyond 3–4 weeks without identifiable cause 5
• Abnormal cells or blasts on peripheral smear 5
• Pancytopenia or unexplained additional cytopenias 5
• Splenomegaly, hepatomegaly, or lymphadenopathy on examination 5
• Systemic constitutional symptoms (fever, weight loss, bone pain) 5

Management Strategy

No Pharmacologic Treatment for the Elevated Platelet Count Itself

Antiplatelet agents (aspirin) and anticoagulation are not indicated for reactive thrombocytosis in children, regardless of platelet magnitude 5, 2. Reactive thrombocytosis is clinically benign and does not increase the risk of thrombotic or hemorrhagic complications, even when platelet counts exceed 1,000 × 10⁹/L 5, 2. No reports of thrombotic complications were found in six studies totaling 1,007 children with secondary thrombocytosis 7.

Treat the Underlying Cause

• If iron deficiency is identified: Initiate oral iron supplementation (elemental iron 3–6 mg/kg/day divided in 2–3 doses) and investigate the source of iron loss (menstrual blood loss, dietary insufficiency, gastrointestinal bleeding, malabsorption) 1
• If infection is present: Provide appropriate antimicrobial therapy 2, 3
• If chronic inflammation is suspected: Refer to the appropriate subspecialist (gastroenterology for inflammatory bowel disease, rheumatology for connective tissue disorders) 3

Activity and Lifestyle

No activity restrictions are necessary; the patient can continue normal activities, including sports 5. The platelet count typically peaks about 2 weeks after the precipitating event and returns to baseline by 3 weeks 5.

Follow-Up and Monitoring

• Routine serial platelet monitoring is not required unless the underlying condition warrants it 5
• Platelet counts generally normalize spontaneously within 2–4 weeks after resolution of the underlying condition 5
• Immediate hematology referral is indicated if platelet count > 600 × 10⁹/L persists beyond 3–4 weeks without an identifiable cause, or if any red-flag features develop 5

Critical Pitfalls to Avoid

• Do not initiate anticoagulation or antiplatelet therapy in reactive thrombocytosis, as it offers no benefit and may cause harm 5
• Do not assume that a platelet count < 1,000 × 10⁹/L excludes primary thrombocythemia; although uncommon in children, essential thrombocythemia can present with counts in the 600–900 × 10⁹/L range 2
• Do not overlook iron deficiency as a cause of extreme thrombocytosis; severe iron deficiency can produce platelet counts exceeding 1,900 × 10⁹/L 6, 4
• Do not skip peripheral smear review by a hematopathologist; automated counters miss critical findings such as giant platelets, schistocytes, or immature white cells 1, 5